Beta 1-subunits are required for regulation of coupling between Ca2+ transients and Ca2+-activated K+ (BK) channels by protein kinase C.
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 beta1-subunit of BK channels. Myocytes from beta1-knockout (beta1-/-) 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 beta1-/- mice. These data show that PKC-dependent regulation of coupling strength between Ca2+ transients and STOCs in colonic myocytes depends upon the interaction between alpha- and beta1-subunits.
Hagen
Brian M
BM
Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV 89557-0046, USA.
Bayguinov
Orline
O
Sanders
Kenton M
KM
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003106:Colon / Q000166:cytology / Q000201:enzymology / Q000378:metabolism / Q000502:physiology; D005260:Female; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D032342:Muscle Cells / Q000166:cytology / Q000201:enzymology / Q000378:metabolism / Q000502:physiology; D024681:Potassium Channels, Calcium-Activated / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D011493:Protein Kinase C / Q000378:metabolism*; D021122:Protein Subunits / Q000172:deficiency / Q000235:genetics / Q000502:physiology
D051036:Large-Conductance Calcium-Activated Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D021122:Protein Subunits; D011493:Protein Kinase C; D002118:Calcium