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MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

₁-Subunits are required for regulation of coupling between Ca²⁺ transients and Ca²⁺-activated K⁺ (BK) channels by protein kinase C

Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada 89557-0046

Submitted 18 April 2003 ; accepted in final form 10 July 2003

Colonic myocytes have spontaneous, localized, Ins (1,4,5) trisphosphate (IP₃) receptor-dependent Ca²⁺ transients that couple to the activation of Ca²⁺-dependent K⁺ channels and spontaneous transient outward currents (STOCs). We previously reported that the coupling strength between spontaneous Ca²⁺ transients and large conductance Ca²⁺ activated K⁺ (BK) channels is regulated by Ca²⁺ influx through nonselective cation channels and activation of protein kinase C (PKC). Here, we used confocal microscopy and the patch-clamp technique to further investigate the coupling between localized Ca²⁺ transients and STOCs in colonic myocytes from animals lacking the regulatory ₁-subunit of BK channels. Myocytes from ₁-knockout (₁^-/-) animals loaded with fluo 4 showed typical localized Ca²⁺ transients, but the STOCs coupled to these events were of abnormally low amplitude. Reduction in external Ca²⁺ or application of inhibitors of nonselective cation channels (SKF-96365) caused no significant change in the amplitude or frequency of STOCs. Likewise, an inhibitor of PKC, GF 109203X, had no significant effect on STOCs. Single-channel recording from BK channels showed that application of an activator (PMA) and an inhibitor (GF 109203X) of PKC did not affect BK channel openings in myocytes of ₁^-/- mice. These data show that PKC-dependent regulation of coupling strength between Ca²⁺ transients and STOCs in colonic myocytes depends upon the interaction between - and ₁-subunits.

calcium puffs; gastrointestinal smooth muscle; colonic motility

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