Article date: February 1996
By: Rainer Büscher, Caterina Heeks, Katsunari Taguchi, Martin C. Michel, in Volume 117, Issue 4, pages 703-711
To elucidate a possible role of species differences in the classification of α1‐adrenoceptor subtypes, we have characterized the α1‐adrenoceptors in guinea‐pig spleen, kidney and cerebral cortex and in bovine cerebral cortex using concentration‐dependent alkylation by chloroethylclonidine and competitive binding with 5‐methylurapidil, methoxamine, (+)‐niguldipine, noradrenaline, oxymetazoline, phentolamine, SDZ NVI‐085, tamsulosin and (+)‐tamsulosin. Rat liver α1B‐adrenoceptors were studied for comparison. Chloroethylclonidine‐sensitivity and (+)‐niguldipine affinity were also compared at cloned rat and bovine α1a‐adrenoceptors.
Chloroethylclonidine concentration‐dependently inactivated α1‐adrenoceptors in all five tissues. While chloroethylclonidine inactivated almost all α1‐adrenoceptors in rat liver and guinea‐pig kidney and brain, 20–30% of α1‐adrenoceptors in guinea‐pig spleen and bovine brain were resistant to alkylation by 10 μm chloroethylclonidine. With regard to concentration‐dependency guinea‐pig kidney and brain were approximately 10 fold less sensitive than guinea‐pig spleen or rat liver.
In rat liver, all drugs tested competed for [3H]‐prazosin binding with steep and monophasic curves. Drug affinities were relatively low and resembled most closely those of cloned rat α1b‐adrenoceptors.
In guinea‐pig spleen, all drugs tested competed for [3H]‐prazosin binding with steep and monophasic curves. Drug affinities were relatively low and resembled most closely those of cloned rat α1b‐adrenoceptors.
In guinea‐pig kidney most drugs tested competed for [3H]‐prazosin binding with steep and monophasic curves and had relatively low drug affinities close to those of cloned rat α1b‐ and α1d‐ adrenoceptors. However, noradrenaline and tamsulosin had consistently biphasic competition curves recognizing 36–39% high and 61–64% low affinity sites.
In guinea‐pig cerebral cortex, all drugs tested competed for [3H]‐prazosin binding with shallow and biphasic curves. While most drugs recognized approximately 25% high affinity sites, tamsulosin and noradrenaline recognized approximately 50% high affinity sites. Drug affinities at the high and low affinity sites except those for tamsulosin and noradrenaline resembled those at cloned α1a‐ and α1b‐adrenoceptors, respectively.
In bovine cerebral cortex all drugs tested except for noradrenaline competed for [3H]‐prazosin binding with shallow and biphasic curves. All drugs recognized approximately 70% high affinity sites. Drug affinities at the high and low affinity sites resembled those at cloned α1a‐ and α1b‐adrenoceptors, respectively. Noradrenaline competition curves in bovine cerebral cortex were steep and monophasic.
When cloned rat and bovine α1a‐adrenoceptors transiently expressed in COS cells were studied in a direct side‐by‐side comparison, both species homologues had similar chloroethylclonidine‐sensitivity and (+)‐niguldipine affinity.
We conclude that properties of bovine α1A‐ and α1B‐adrenoceptors are very similar to those of other species such as rat. α1‐Adrenoceptor subtypes in guinea‐pigs resemble α1A‐ and α1B‐adrenoceptors in other species but chloroethylclonidine sensitivity and competition binding profiles of noradrenaline and tamsulosin are not compatible with previously established α1‐adrenoceptor subtype classification.
To elucidate a possible role of species differences in the classification of α1‐adrenoceptor subtypes, we have characterized the α1‐adrenoceptors in guinea‐pig spleen, kidney and cerebral cortex and in bovine cerebral cortex using concentration‐dependent alkylation by chloroethylclonidine and competitive binding with 5‐methylurapidil, methoxamine, (+)‐niguldipine, noradrenaline, oxymetazoline, phentolamine, SDZ NVI‐085, tamsulosin and (+)‐tamsulosin. Rat liver α1B‐adrenoceptors were studied for comparison. Chloroethylclonidine‐sensitivity and (+)‐niguldipine affinity were also compared at cloned rat and bovine α1a‐adrenoceptors.
Chloroethylclonidine concentration‐dependently inactivated α1‐adrenoceptors in all five tissues. While chloroethylclonidine inactivated almost all α1‐adrenoceptors in rat liver and guinea‐pig kidney and brain, 20–30% of α1‐adrenoceptors in guinea‐pig spleen and bovine brain were resistant to alkylation by 10 μm chloroethylclonidine. With regard to concentration‐dependency guinea‐pig kidney and brain were approximately 10 fold less sensitive than guinea‐pig spleen or rat liver.
In rat liver, all drugs tested competed for [3H]‐prazosin binding with steep and monophasic curves. Drug affinities were relatively low and resembled most closely those of cloned rat α1b‐adrenoceptors.
In guinea‐pig spleen, all drugs tested competed for [3H]‐prazosin binding with steep and monophasic curves. Drug affinities were relatively low and resembled most closely those of cloned rat α1b‐adrenoceptors.
In guinea‐pig kidney most drugs tested competed for [3H]‐prazosin binding with steep and monophasic curves and had relatively low drug affinities close to those of cloned rat α1b‐ and α1d‐ adrenoceptors. However, noradrenaline and tamsulosin had consistently biphasic competition curves recognizing 36–39% high and 61–64% low affinity sites.
In guinea‐pig cerebral cortex, all drugs tested competed for [3H]‐prazosin binding with shallow and biphasic curves. While most drugs recognized approximately 25% high affinity sites, tamsulosin and noradrenaline recognized approximately 50% high affinity sites. Drug affinities at the high and low affinity sites except those for tamsulosin and noradrenaline resembled those at cloned α1a‐ and α1b‐adrenoceptors, respectively.
In bovine cerebral cortex all drugs tested except for noradrenaline competed for [3H]‐prazosin binding with shallow and biphasic curves. All drugs recognized approximately 70% high affinity sites. Drug affinities at the high and low affinity sites resembled those at cloned α1a‐ and α1b‐adrenoceptors, respectively. Noradrenaline competition curves in bovine cerebral cortex were steep and monophasic.
When cloned rat and bovine α1a‐adrenoceptors transiently expressed in COS cells were studied in a direct side‐by‐side comparison, both species homologues had similar chloroethylclonidine‐sensitivity and (+)‐niguldipine affinity.
We conclude that properties of bovine α1A‐ and α1B‐adrenoceptors are very similar to those of other species such as rat. α1‐Adrenoceptor subtypes in guinea‐pigs resemble α1A‐ and α1B‐adrenoceptors in other species but chloroethylclonidine sensitivity and competition binding profiles of noradrenaline and tamsulosin are not compatible with previously established α1‐adrenoceptor subtype classification.
DOI: 10.1111/j.1476-5381.1996.tb15247.x
View this article