title: Effect of acidosis on tension and [Ca2+]i in rat cerebral arteries: is there a role for membrane potential?
abstract: The cellular mechanism responsible for the reduction of tension in cerebral small arteries to acidosis is not known. In this study the role of smooth muscle intracellular Ca2+ concentration ([Ca2+]i) and membrane potential for the relaxation to acidosis was investigated in isolated rat cerebral small arteries. Isometric force was measured simultaneously with [Ca2+]i (fura 2) or with membrane potential (intracellular microelectrodes), and acidosis was induced by increasing PCO2 or reducing HCO3- of the bathing solution. Both hypercapnic and normocapnic acidosis were associated with a reduction of intracellular pH [measured with 2',7'-bis-(carboxyethyl)-5 (and -6)-carboxyfluorescein], caused relaxation, and reduced [Ca2+]i. However, whereas hypercapnic acidosis caused hyperpolarization, normocapnic acidosis was associated with depolarization. It is concluded that a reduction of [Ca2+]i is in part responsible for the direct effect of the acidosis on the vascular smooth muscle both during normo- and hypercapnia. The mechanism responsible for the reduction of [Ca2+]i differs between the hypercapnic and normocapnic acidosis, being partly explained by hyperpolarization during hypercapnic acidosis, whereas it is seen despite depolarization during normocapnic acidosis.
authors.affiliation: Department of Pharmacology, University of Aarhus, Denmark.
authors.forename: H L
authors.initials: HL
authors.lastname: Peng
authors.forename: P E
authors.initials: PE
authors.lastname: Jensen
authors.forename: H
authors.initials: H
authors.lastname: Nilsson
authors.forename: C
authors.initials: C
authors.lastname: Aalkjaer
mesh_terms: D000138:Acidosis / Q000503:physiopathology*; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002245:Carbon Dioxide / Q000494:pharmacology; D002536:Cerebral Arteries / Q000503:physiopathology*; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D006935:Hypercapnia; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials; D009119:Muscle Contraction; D009131:Muscle, Smooth, Vascular / Q000503:physiopathology*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D001639:Bicarbonates; D005452:Fluoresceins; D005456:Fluorescent Dyes; D002245:Carbon Dioxide; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D002118:Calcium