Article date: December 1991
By: Jean C. Hardwick, Lisa M. Coniglio, Rodney L. Parsons, in Volume 104, Issue 4, pages 879-886
The effect of the protein kinase inhibitor, staurosporine, on the extent and time course of recovery following carbachol‐induced desensitization was studied in snake twitch‐muscle fibres maintained in an isotonic potassium propionate solution and voltage‐clamped to +30mV.
Pretreatment with staurosporine (0.5 μm) decreased the extent of recovery of spontaneous miniature endplate current (m.e.p.c.) amplitudes following desensitization by a sustained application of 540 μm carbachol. Recovery was inhibited by approximately 50% without altering the time course of m.e.p.c. recovery.
Staurosporine also produced a concentration‐dependent (10 nm to 0.5 μm) decrease in the amplitude of a second carbachol‐induced current, following a wash period, as compared to the amplitude of the current produced by the initial carbachol application. Pretreatment with 0.5 μm K252a, another wide spectrum protein kinase inhibitor, also decreased the extent of recovery of the response to a second carbachol application following desensitization.
Staurosporine pretreatment (0.5 μm) had no effect on either the kinetics of receptor‐channel gating or the initial endplate sensitivity to agonist. This was determined by comparing the amplitude of the carbachol (540 μm)‐induced currents and the amplitude and decay rate of m.e.p.cs in control and staurosporine‐treated fibres.
Staurosporine had no effect on the time course of desensitization onset produced during the initial application of 540 μm carbachol or the depth of desensitization produced by the end of a 2–3 min exposure to 540 μm carbachol.
Elevation of the external calcium concentration from 1 to 10 mm during the 540 μm carbachol application completely antagonized the decreased extent of recovery of m.e.p.c. amplitude produced by pretreatment with 0.5 μm staurosporine.
We suggest that phosphorylation of a population of acetylcholine receptors is required for complete recovery from desensitization, and that staurosporine inhibits the protein kinases responsible for this phosphorylation.
We further propose that a transient increase in intracellular calcium, produced by an increase in calcium influx through agonist‐activated endplate channels, stimulates additional protein kinase activity, which in turn, antagonizes the effect of staurosporine‐treatment on recovery.
The effect of the protein kinase inhibitor, staurosporine, on the extent and time course of recovery following carbachol‐induced desensitization was studied in snake twitch‐muscle fibres maintained in an isotonic potassium propionate solution and voltage‐clamped to +30mV.
Pretreatment with staurosporine (0.5 μm) decreased the extent of recovery of spontaneous miniature endplate current (m.e.p.c.) amplitudes following desensitization by a sustained application of 540 μm carbachol. Recovery was inhibited by approximately 50% without altering the time course of m.e.p.c. recovery.
Staurosporine also produced a concentration‐dependent (10 nm to 0.5 μm) decrease in the amplitude of a second carbachol‐induced current, following a wash period, as compared to the amplitude of the current produced by the initial carbachol application. Pretreatment with 0.5 μm K252a, another wide spectrum protein kinase inhibitor, also decreased the extent of recovery of the response to a second carbachol application following desensitization.
Staurosporine pretreatment (0.5 μm) had no effect on either the kinetics of receptor‐channel gating or the initial endplate sensitivity to agonist. This was determined by comparing the amplitude of the carbachol (540 μm)‐induced currents and the amplitude and decay rate of m.e.p.cs in control and staurosporine‐treated fibres.
Staurosporine had no effect on the time course of desensitization onset produced during the initial application of 540 μm carbachol or the depth of desensitization produced by the end of a 2–3 min exposure to 540 μm carbachol.
Elevation of the external calcium concentration from 1 to 10 mm during the 540 μm carbachol application completely antagonized the decreased extent of recovery of m.e.p.c. amplitude produced by pretreatment with 0.5 μm staurosporine.
We suggest that phosphorylation of a population of acetylcholine receptors is required for complete recovery from desensitization, and that staurosporine inhibits the protein kinases responsible for this phosphorylation.
We further propose that a transient increase in intracellular calcium, produced by an increase in calcium influx through agonist‐activated endplate channels, stimulates additional protein kinase activity, which in turn, antagonizes the effect of staurosporine‐treatment on recovery.
DOI: 10.1111/j.1476-5381.1991.tb12521.x
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