Depolarization-induced calcium influx in rat mesenteric small arterioles is mediated exclusively via mibefradil-sensitive calcium channels.
1. In this study, intracellular Ca(2+) was measured as the Fura-2 ratio (R) of fluorescence excited at 340 and 380 nm (F(340)/F(380)) in nonpressurized rat mesenteric small arterioles ( (lumen diameter) 10-25 microm). 2. The response to depolarization using 75 mm KCl was an increase in R from a baseline of 0.96+/-0.01 ([Ca(2+)](i) approximately 74 nm) to 1.04+/-0.01 ( approximately 128 nm) (n=80). The response to 75 mm K(+) was reversibly abolished in Ca(2+)-free physiological saline solution, whereas phentolamine (10 microm) or tetrodotoxin (1 microm) had no effects. LaCl(3) (200 microm) inhibited 61+/-9% of the response. 3. A [K(+)]-response curve indicated that the Ca(2+) response was activated between 15 and 25 mm K(+). The data suggest that the Ca(2+) response was caused by the activation of voltage-dependent Ca(2+) channels. 4. Mibefradil use dependently inhibited the Ca(2+) response to 75 mm K(+) by 29+/-2% (100 nm), 73+/-7% (1 microm) or 89+/-7% (10 microm). Pimozide (500 nm) use dependently inhibited the Ca(2+) response by 85+/-1%. 5. Nifedipine (1 microm) inhibited the Ca(2+) response to 75 mm K(+) by 41+/-12%. The response was not inhibited by calciseptine (500 nm), omega-agatoxin IVA (100 nm), omega-conotoxin MVIIA (500 nm), or SNX-482 (100 nm). 6. Using reverse transcriptase-polymerase chain reaction, it was shown that neither Ca(V)2.1a (P-type) nor Ca(V)2.1b (Q-type) voltage-dependent Ca(2+) channels were expressed in mesenteric arterioles, whereas the Ca(V)3.1 (T-type) channel was expressed. Furthermore, no amplification products were detected when using specific primers for the beta(1b), beta(2), or beta(3) auxiliary subunits of high-voltage-activated Ca(2+) channels. 7. The results suggest that the voltage-dependent Ca(2+) channel activated by sustained depolarization in mesenteric arterioles does not classify as any of the high-voltage-activated channels (L-, P/Q-, N-, or R-type), but is likely to be a T-type channel. The possibility that the sustained Ca(2+) influx observed was the result of a T-type window current is discussed.
Jensen
Lars J
LJ
Department of Medical Physiology, The Panum Institute, University of Copenhagen, Copenhagen DK-2200, Denmark. ljj@mfi.ku.dk
Salomonsson
Max
M
Jensen
Boye L
BL
Holstein-Rathlou
Niels-Henrik
NH
D000818:Animals; D001160:Arterioles / Q000033:anatomy & histology / Q000187:drug effects / Q000648:ultrastructure; D015139:Blotting, Southern / Q000379:methods; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects* / Q000502:physiology; D003718:Denmark; D004546:Elapid Venoms / Q000494:pharmacology; D005453:Fluorescence; D016257:Fura-2 / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects / Q000502:physiology; D007811:Lanthanum / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000502:physiology*; D008638:Mesenteric Arteries / Q000033:anatomy & histology / Q000187:drug effects* / Q000502:physiology*; D020748:Mibefradil / Q000494:pharmacology*; D009131:Muscle, Smooth, Vascular / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology; D009543:Nifedipine / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D010868:Pimozide / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D019831:Sodium-Calcium Exchanger / Q000378:metabolism; D012996:Solutions / Q000737:chemistry; D013111:Spider Venoms / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D020867:omega-Agatoxin IVA / Q000494:pharmacology; D020960:omega-Conotoxins / Q000494:pharmacology
D015220:Calcium Channels; D004546:Elapid Venoms; C115521:SNX 482; D019831:Sodium-Calcium Exchanger; D012996:Solutions; D013111:Spider Venoms; D020867:omega-Agatoxin IVA; D020960:omega-Conotoxins; C028521:lanthanum chloride; D010868:Pimozide; D020748:Mibefradil; C067971:calciseptine; D013779:Tetrodotoxin; D011189:Potassium Chloride; D007811:Lanthanum; C078452:ziconotide; D009543:Nifedipine; D002118:Calcium; D016257:Fura-2; D010646:Phentolamine