Hyperpolarization, but not depolarization, increases intracellular Ca(2+) level in cultured chick myoblasts.
Ca(2+) influx appears to be important for triggering myoblast fusion. It remains, however, unclear how Ca(2+) influx rises prior to myoblast fusion. The present study examines a possible involvement of the voltage-dependent Ca(2+) influx pathways. Treatment with the L-type Ca(2+) channel blockers, diltiazem, and nifedipine did not alter cytosolic Ca(2+) levels. Depolarization with high K(+) solution and activation of Ca(2+) channel with Bay K 8644, and agonist of voltage dependent Ca(2+) channels, failed to elicit increases intracellular Ca(2+) level, indicating the absence of depolarization-operated mechanisms. In contrast, phloretin, an agonist of Ca(2+)-activated potassium (K(Ca)) channels, was able to hyperpolarize membrane potential and promoted Ca(2+) influx. These effects were completely abolished by treatment of charybdotoxin, a specific inhibitor of K(Ca) channels. In addition, gadolinium, a potent stretch-activated channel (SAC) blocker, prevented the phloretin-mediated Ca(2+) increase, indicating the involvement of SACs in Ca(2+) influx. Furthermore, phloretin stimulated precocious myoblast fusion and this effect was blocked with gadolinium or charybdotoxin. Taken together, these results suggest that induced hyperpolarization, but not depolarization increases Ca(2+) influx through stretch-activated channels, and in turn triggers myoblast fusion.
Park
Jae-Yong
JY
School of Biological Sciences, Seoul National University, Seoul, 151-742, Korea.
Lee
Doyun
D
Maeng
Ji-Ung
JU
Koh
Duk-Su
DS
Kim
Kyungjin
K
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002478:Cells, Cultured; D018999:Charybdotoxin / Q000494:pharmacology; D002642:Chick Embryo; D005682:Gadolinium / Q000494:pharmacology; D007424:Intracellular Fluid / Q000378:metabolism; D008561:Membrane Fusion / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010693:Phloretin / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism
D015220:Calcium Channels; D015221:Potassium Channels; D018999:Charybdotoxin; D005682:Gadolinium; D010693:Phloretin; D002118:Calcium