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Activators of protein kinase C decrease Ca2+ spark frequency in smooth muscle cells from cerebral arteries.

Bonev A, Jaggar J, Rubart M, Nelson MT

American Journal of Physiology-Cell Physiology. 1997;273( 6 Pt 1):C2090-5.

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Abstract

Local Ca2+ transients ("Ca2+ sparks") caused by the opening of one or the coordinated opening of a number of tightly clustered ryanodine-sensitive Ca(2+)-release (RyR) channels in the sarcoplasmic reticulum (SR) activate nearby Ca(2+)-dependent K+ (KCa) channels to cause an outward current [referred to as a "spontaneous transient outward current" (STOC)]. These KCa currents cause membrane potential hyperpolarization of arterial myocytes, which would lead to vasodilation through decreasing Ca2+ entry through voltage-dependent Ca2+ channels. Therefore, modulation of Ca2+ spark frequency should be a means to regulation of KCa channel currents and hence membrane potential. We examined the frequency modulation of Ca2+ sparks and STOCs by activation of protein kinase C (PKC). The PKC activators, phorbol 12-myristate 13-acetate (PMA; 10 nM) and 1,2-dioctanoyl-sn-glycerol (1 microM), decreased Ca2+ spark frequency by 72% and 60%, respectively, and PMA reduced STOC frequency by 83%. PMA also decreased STOC amplitude by 22%, which could be explained by an observed reduction (29%) in KCa channel open probability in the absence of Ca2+ sparks. The reduction in STOC frequency occurred in the presence of an inorganic blocker (Cd2+) of voltage-dependent Ca2+ channels. The reduction in Ca2+ spark frequency did not result from SR Ca2+ depletion, since caffeine-induced Ca2+ transients did not decrease in the presence of PMA. These results suggest that activators of PKC can modulate the frequency of Ca2+ sparks, through an effect on the RyR channel, which would decrease STOC frequency (i.e., KCa channel activity).

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Place of publication:
UNITED STATES
Volume:
273( 6 Pt 1)
Start page:
C2090
End page:
5
Pagination:
C2090-5
Access state:
Active

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Manchester eScholar ID:
uk-ac-man-scw:1d16417
Created:
30th August, 2009, 13:57:03
Last modified:
3rd March, 2010, 17:07:57

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