Article date: May 1993
By: Minori Mitsui, Hideaki Karaki, in Volume 109, Issue 1, pages 229-233
Effects of phorbol esters on the cytosolic Ca2+ level ([Ca2+]i) and muscle tension in the intestinal smooth muscle of guinea‐pig taenia caeci were examined.
12‐Deoxyphorbol 13‐isobutyrate (DPB, 1 μm) did not change the [Ca2+]i and tension in resting muscle.
In high K+‐stimulated muscle, 1 μm DPB transiently augmented the contraction and decreased [Ca2+]i. 12‐Deoxyphorbol 13‐isobutyrate 20‐acetate (1 μm) and phorbol 12, 13‐dibutyrate (1 μm) showed similar effects to DPB whereas phorbol 12‐myristate 13‐acetate (1 μm) and phorbol 12, 13‐didecanoate (1 μm) were ineffective.
DPB (1 μm) inhibited both [Ca2+]i and tension stimulated by 300 nm carbachol or 3 μm histamine. In the presence of a higher concentration of carbachol (1 μm), DPB decreased [Ca2+]i and transiently increased muscle tension.
In the muscle strips permeabilized with bacterial α‐toxin, 1 μm DPB shifted the Ca2+‐tension curve to the left. An inhibitor of protein kinase C, H‐7 (30 μm), inhibited the effect of DPB.
DPB did not change the high K+‐induced contraction in the muscle strips pretreated with 3 μm phorbol 12‐myristate 13‐acetate for 24 h.
These results suggest that activation of protein kinase C has dual effects; it augments contraction by increasing the Ca2+ sensitivity of the contractile elements and it inhibits contraction by decreasing [Ca2+]i.
Effects of phorbol esters on the cytosolic Ca2+ level ([Ca2+]i) and muscle tension in the intestinal smooth muscle of guinea‐pig taenia caeci were examined.
12‐Deoxyphorbol 13‐isobutyrate (DPB, 1 μm) did not change the [Ca2+]i and tension in resting muscle.
In high K+‐stimulated muscle, 1 μm DPB transiently augmented the contraction and decreased [Ca2+]i. 12‐Deoxyphorbol 13‐isobutyrate 20‐acetate (1 μm) and phorbol 12, 13‐dibutyrate (1 μm) showed similar effects to DPB whereas phorbol 12‐myristate 13‐acetate (1 μm) and phorbol 12, 13‐didecanoate (1 μm) were ineffective.
DPB (1 μm) inhibited both [Ca2+]i and tension stimulated by 300 nm carbachol or 3 μm histamine. In the presence of a higher concentration of carbachol (1 μm), DPB decreased [Ca2+]i and transiently increased muscle tension.
In the muscle strips permeabilized with bacterial α‐toxin, 1 μm DPB shifted the Ca2+‐tension curve to the left. An inhibitor of protein kinase C, H‐7 (30 μm), inhibited the effect of DPB.
DPB did not change the high K+‐induced contraction in the muscle strips pretreated with 3 μm phorbol 12‐myristate 13‐acetate for 24 h.
These results suggest that activation of protein kinase C has dual effects; it augments contraction by increasing the Ca2+ sensitivity of the contractile elements and it inhibits contraction by decreasing [Ca2+]i.
DOI: 10.1111/j.1476-5381.1993.tb13558.x
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