L-type and Ca super(2+) release channel-dependent hierarchical Ca super(2+) signalling in rat portal vein myocytes

• Published in: Cell calcium (Edinburgh) Vol. 22; no. 5; pp. 399 - 411
• Main Authors: Arnaudeau, S, Boittin, F X, Macrez, N, Lavie, J L, Mironneau, C, Mironneau, J
• Format: Journal Article
• Language: English
• Published: 01.11.1997
• ISSN: 0143-4160

Ca super(2+) signalling events and whole-cell Ca super(2+) 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 Ca super(2+) store was depleted or Ca super(2+) release channels were blocked by 10 mu M ryanodine, inward Ca super(2+) currents induced slow and sustained elevations of [Ca super(2+)] sub(i). These Ca super(2+) responses were suppressed by 1 mu M oxodipine and by depolarizations to +120 mV, a potential close to the reversal potential for Ca super(2+) ions, suggesting that they reflected Ca super(2+) influx through L-type Ca super(2+) channels. With functioning intracellular Ca super(2+) stores, flash photolysis of caged Ca super(2+) gave rise to a small increase in [Ca super(2+)] sub(i) with superimposed Ca super(2+) sparks, reflecting the opening of clustered Ca super(2+) release channels. Brief Ca super(2+) currents in the voltage range from -30 to +10 mV triggered Ca super(2+) sparks or macrosparks that did not propagate in the entire line-scan image. Increasing the duration of Ca super(2+) current for 100 ms or more allowed the trigger of propagating Ca super(2+) waves which originated from the same initiation sites as the caffeine-activated response. Both Ca super(2+) sparks and initiation sites of Ca super(2+) waves activated by Ca super(2+) currents were observed in the vicinity of areas that excluded the Ca super(2+) probes, reflecting infoldings of the plasma membrane close to the sarcoplasmic reticulum, as revealed by fluorescent markers. The hierarchy of Ca super(2+) signalling events, from submicroscopic fundamental events to elementary events (sparks) and propagated waves, provides an integrated mechanism to regulate vascular tone.