Critical intracellular Ca2+ concentration for all-or-none Ca2+ spiking in single smooth muscle cells.
Neurotransmitters induce contractions of smooth muscle cells initially by mobilizing Ca2+ from intracellular Ca2+ stores through inositol 1,4,5-trisphosphate (InsP3) receptors. Here we studied roles of the molecules involved in Ca2+ mobilization in single smooth muscle cells. A slow rise in cytoplasmic Ca2+ ([Ca2+]i) in agonist-stimulated smooth muscle cells was followed by a wave of rapid regenerative Ca2+ release as the local [Ca2+]i reached a critical concentration of approximately 160 nM. Neither feedback regulation of phospholipase C nor caffeine-sensitive Ca(2+)-induced Ca2+ release was found to be required in the regenerative Ca2+ release. These results indicate that Ca(2+)-dependent feedback control of InsP3-induced Ca2+ release plays a dominant role in the generation of the regenerative Ca2+ release. The resulting Ca2+ release in a whole cell was an all-or-none event, i.e. constant peak [Ca2+]i was attained with agonist concentrations above the threshold value. This finding suggests a possible digital mode involved in the neural control of smooth muscle contraction.
Iino
M
M
Department of Pharmacology, Faculty of Medicine, University of Tokyo, Japan.
Yamazawa
T
T
Miyashita
Y
Y
Endo
M
M
Kasai
H
H
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000502:physiology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000502:physiology*; D012433:Ryanodine / Q000494:pharmacology; D013621:Taenia / Q000166:cytology
D012433:Ryanodine; D002118:Calcium