Relationship between global cytosolic Ca2+ concentration and Ca2+-activated K+ current in rabbit cerebral arterial myocyte.
In smooth muscle cells, the sarcoplasmic reticulum (SR) has been identified as the primary storage site for intracellular Ca2+. The peripheral SR is in close proximity with plasma membrane to make a narrow subsarcolemmal space. In this study, we investigated the regulation of subsarcolemmal [Ca2+] ([Ca2+]sl) and global cytosolic [Ca2+] ([Ca2+]c) of rabbit arterial smooth muscle using whole cell patch clamp technique and microspectrofluorimetry. The Ca2+-activated K+ current (IK(Ca)) and the ratio of fura-2 fluorescence (R340/380) were considered to reflect the [Ca2+]sl and [Ca2+]c, respectively. At a holding potential of 0 mV, extracellular application of 10 mM caffeine, a well known Ca2+-releasing agent, induced transient increase of IK(Ca) and R340/380 (IK(Ca)-transient and R340/380-transient, respectively). The increase and decay of IK(Ca) transient was faster than R340/380-transient. By repetitive application of caffeine, when the refilling state of SR was supposed to be lower than the control condition, IK(Ca)-transient and R340/380 transient were suppressed to different levels; e.g. the second application 20 sec after the first could induce smaller IK(Ca) transient than R340/380-transient. Dissociation of IK(Ca)-transient and R340/380-transient was removed by sufficient (>3 min) washout of caffeine. Recovery from the dissociation was also dependent upon the membrane potential; faster recovery was observed at negative (-40 mV) holding potential than at depolarized (0 mV) condition. Dissociation of IK(Ca) from [Ca2+]c was also partially prevented by perfusion with Na+-free (replaced by NMDG+) extracellular solution. These results suggest that, 1) there is prominent spatial inhomogeneity of [Ca2+] in cerebral arterial myocyte, 2) [Ca2+]Sl is preferentially affected by the interference from nearby plasmalemmal Ca2+ regulation mechanism which is partly dependent upon extracellular Na+.
Kim
S J
SJ
Department of Physiology & Biophysics, Seoul National University College of Medicine, Korea.
Ahn
J M
JM
Kim
Y C
YC
Park
S J
SJ
Choi
J Y
JY
Suh
S H
SH
So
I
I
Kim
K W
KW
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D002536:Cerebral Arteries / Q000187:drug effects / Q000502:physiology; D003600:Cytosol; D004594:Electrophysiology; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000502:physiology; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology; D011817:Rabbits
D000697:Central Nervous System Stimulants; D015221:Potassium Channels; D002110:Caffeine; D002118:Calcium