Coupling strength between localized Ca2+ transients and K+ channels is regulated by protein kinase C

Localized Ca2+ transients resulting from inositol trisphosphate (IP3)-dependent Ca2+ release couple to spontaneous transient outward currents (STOCs) in murine colonic myocytes. Confocal microscopy and whole cell patch-clamp techniques were used to investigate coupling between localized Ca2+ transients and STOCs. Colonic myocytes were loaded with fluo 3. Reduction in external Ca2+ ([ Ca2+](o)) reduced localized Ca2+ transients but increased STOC amplitude and frequency. Simultaneous recordings of Ca2+ transients and STOCs showed increased coupling strength between Ca2+ transients and STOCs when [Ca2+](o) was reduced. Gd3+ (10 muM) did not affect Ca2+ transients but increased STOC amplitude and frequency. Similarly, an inhibitor of Ca2+ influx, 1-2-(4-methoxyphenyl)-2-[3-(4-methoxyphenyl) propoxy]ethyl-1H-imidazole (SKF-96365), increased STOC amplitude and frequency. A protein kinase C (PKC) inhibitor, GF-109203X, also increased the amplitude and frequency of STOCs but had no effect on Ca2+ transients. Phorbol 12-myristate 13-acetate (1 muM) reduced STOC amplitude and frequency but did not affect Ca2+ transients. 4 alpha -Phorbol (1 muM) had no effect on STOCs or Ca2+ transients. Single channel studies indicated that large-conductance Ca2+-activated K+ (BK) channels were inhibited by a Ca2+-dependent PKC. In summary 1) Ca2+ release from IP3 receptor-operated stores activates Ca2+-activated K+ channels; 2) Ca2+ influx through nonselective cation channels facilitates activation of PKC; and 3) PKC reduces the Ca2+ sensitivity of BK channels, reducing the coupling strength between localized Ca2+ transients and BK channels.