Increases in cytosolic free Ca2+ induced by ATP, complement and beta-lipoprotein in mouse L fibroblasts.
By means of Ca2+- and K+-selective microelectrodes, the changes in intracellular free Ca2+ and K+ were measured during the hyperpolarizing responses induced by ATP, complement and beta-lipoprotein in mouse fibroblastic L cells. The cytoplasmic Ca2+ concentration [( Ca]i) was about 0.4 microM in the resting state. The hyperpolarizing responses always coincided with a phasic increase in [Ca]i. ATP or beta-lipoprotein induced about a 2-fold rise in [Ca]i, and complement did up to 3-fold. Both the hyperpolarizing responses and [Ca]i increases were prevented by removal of external Ca2+ or by application of a Ca-channel blocker, nifedipine. Quinine, a Ca-activated K-channel inhibitor, suppressed the hyperpolarizing responses but not the [Ca]i increases. During the hyperpolarizing response, the intracellular free K+ concentration gradually decreased from about 120 to 110 mM. Thus, it is concluded that ATP, complement and beta-lipoprotein caused a transient elevation of cytoplasmic free Ca2+ due to Ca2+ influxes, thereby inducing electrical membrane responses through activation of Ca-dependent K-channels in the fibroblasts.
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D003165:Complement System Proteins / Q000494:pharmacology*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008839:Microelectrodes; D009543:Nifedipine / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D011803:Quinine / Q000494:pharmacology
D008077:Lipoproteins, LDL; D004533:Egtazic Acid; D000255:Adenosine Triphosphate; D003165:Complement System Proteins; D011803:Quinine; D009543:Nifedipine; D011188:Potassium; D002118:Calcium