Conducted vasoconstriction in rat mesenteric arterioles: role for dihydropyridine-insensitive Ca(2+) channels.
The aim of this study was to evaluate the role of voltage-operated Ca(2+) channels in the initiation and conduction of vasoconstrictor responses to local micropipette electrical stimulation of rat mesenteric arterioles (28 +/- 1 microm, n = 79) in vivo. Local and conducted (600 microm upstream from the pipette) vasoconstriction was not blocked by TTX (1 micromol/l, n = 5), nifedipine, or nimodipine (10 micromol/l, n = 9). Increasing the K(+) concentration of the superfusate to 75 mmol/l did not evoke vasoconstriction, but this depolarizing stimulus reversibly abolished vasoconstrictor responses to current stimulation (n = 7). Addition of the T-type Ca(2+) antagonist mibefradil (10 micromol/l, n = 6) to the superfusate reversibly blocked local and conducted vasoconstriction to current stimulation. With the use of RT-PCR techniques, it was demonstrated that rat mesenteric arterioles <40 microm do not express mRNA for L-type Ca(2+) channels (alpha(1C)-subunit), whereas mRNA coding for T-type subunits was found (alpha(1G)- and alpha(1H)-subunits). The data indicate that L-type Ca(2+) channels are absent from rat mesenteric arterioles (<40 microm). Rather, the vasoconstrictor responses appear to rely on other types of voltage-gated, dihydropyridine-insensitive Ca(2+) channels, possibly of the T-type.
Gustafsson
F
F
Division of Renal and Cardiovascular Research, Department of Medical Physiology, Panum Institute, University of Copenhagen, DK-2200 Copenhagen, Denmark.
Andreasen
D
D
Salomonsson
M
M
Jensen
B L
BL
Holstein-Rathlou
N
N
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000235:genetics / Q000378:metabolism*; D020747:Calcium Channels, T-Type / Q000235:genetics / Q000378:metabolism*; D004095:Dihydropyridines / Q000494:pharmacology; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression; D008297:Male; D008638:Mesenteric Arteries / Q000737:chemistry / Q000502:physiology*; D020748:Mibefradil / Q000494:pharmacology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009532:Nickel / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013779:Tetrodotoxin / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*
D000317:Adrenergic alpha-Antagonists; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D020747:Calcium Channels, T-Type; D004095:Dihydropyridines; D004791:Enzyme Inhibitors; D012333:RNA, Messenger; D020748:Mibefradil; D013779:Tetrodotoxin; C022838:nickel chloride; D009532:Nickel; D011188:Potassium; D019331:NG-Nitroarginine Methyl Ester; D009638:Norepinephrine; D010646:Phentolamine