Ca2+ sparks and Ca2+ waves activate different Ca(2+)-dependent ion channels in single myocytes from rat portal vein.
Ca2+ release from intracellular stores was examined with the use of a confocal microscope in single, voltage-clamped myocytes from rat portal vein loaded with both Fluo-3 and Fura-red. Spontaneous local increases in [Ca2+]i from the sarcoplasmic reticulum, termed Ca2+ sparks, were observed in about 30% of the quiescent cells tested. Ca2+ sparks could be evoked by low concentrations of caffeine (1 mM) or ryanodine (1 microM). Both spontaneous and caffeine-evoked Ca2+ sparks were insensitive to blockers of voltage-dependent Ca2+ channels. Caffeine (10 mM) triggered propagating Ca2+ waves of large amplitude which started from the same site than spontaneous Ca2+ sparks in 73% of the cells, as expected if Ca2+ sparks were the elementary events that could account for the initiation of Ca2+ waves. Spontaneous Ca2+ sparks activated both Ca(2+)-dependent K+ and non-selective cation currents, whereas Ca2+ waves were able to evoke Ca(2+)-dependent chloride current. These results suggest that both inward cation current and outward K+ current activated by Ca2+ sparks may exert a key role in controlling the basal activity of vascular myocytes.
Laboratoire de Physiologie Cellulaire et Pharmacologie Moléculaire, CNRS ESA 5017, Université de Bordeaux II, France.
J
J
Mironneau
S
S
Arnaudeau
N
N
Macrez-Lepretre
F X
FX
Boittin
D000814:Aniline Compounds; D000818:Animals; D001572:Benzofurans; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology*; D005071:Evoked Potentials; D005456:Fluorescent Dyes; D006321:Heart / Q000502:physiology*; D007093:Imidazoles; D018613:Microscopy, Confocal; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism; D011169:Portal Vein; D051381:Rats; D017208:Rats, Wistar; D014966:Xanthenes
D000814:Aniline Compounds; D001572:Benzofurans; D015220:Calcium Channels; D005456:Fluorescent Dyes; D007093:Imidazoles; D014966:Xanthenes; C082877:fura red; C059715:Fluo-3; D002110:Caffeine; D002118:Calcium