L-type and Ca2+ release channel-dependent hierarchical Ca2+ signalling in rat portal vein myocytes.
Ca2+ signalling events and whole-cell Ca2+ currents were analyzed in single myocytes from rat portal vein by using a laser scanning confocal microscope combined with the patch-clamp technique. In myocytes in which the intracellular Ca2+ store was depleted or Ca2+ release channels were blocked by 10 microM ryanodine, inward Ca2+ currents induced slow and sustained elevations of [Ca2+]i. These Ca2+ responses were suppressed by 1 microM oxodipine and by depolarizations to +120 mV, a potential close to the reversal potential for Ca2+ ions, suggesting that they reflected Ca2+ influx through L-type Ca2+ channels. With functioning intracellular Ca2+ stores, flash photolysis of caged Ca2+ gave rise to a small increase in [Ca2+]i with superimposed Ca2+ sparks, reflecting the opening of clustered Ca2+ release channels. Brief Ca2+ currents in the voltage range from -30 to +10 mV triggered Ca2+ sparks or macrosparks that did not propagate in the entire line-scan image. Increasing the duration of Ca2+ current for 100 ms or more allowed the trigger of propagating Ca2+ waves which originated from the same initiation sites as the caffeine-activated response. Both Ca2+ sparks and initiation sites of Ca2+ waves activated by Ca2+ currents were observed in the vicinity of areas that excluded the Ca2+ probes, reflecting infoldings of the plasma membrane close to the sarcoplasmic reticulum, as revealed by fluorescent markers. The hierarchy of Ca2+ signalling events, from submicroscopic fundamental events to elementary events (sparks) and propagated waves, provides an integrated mechanism to regulate vascular tone.
Arnaudeau
S
S
Laboratoire de Physiologie Cellulaire et Pharmacologie Moléculaire, CNRS ESA 5017, Université de Bordeaux II, France.
Boittin
F X
FX
Macrez
N
N
Lavie
J L
JL
Mironneau
C
C
Mironneau
J
J
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D004594:Electrophysiology; D007425:Intracellular Membranes / Q000378:metabolism; D011169:Portal Vein / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000378:metabolism* / Q000502:physiology; D015398:Signal Transduction
D015220:Calcium Channels; D002118:Calcium