Heterogeneity in cytosolic calcium regulation among different microvascular smooth muscle cells of the rat retina.
Rat retinae were dissociated to yield intact microvessels 7 to 42 microm in diameter. These were loaded with fura-2 AM and single fragments anchored down in a recording bath. Intracellular Ca(2+) levels from 20- to 30-microm sections of vessel were estimated by microfluorimetry. The vessels studied were identified as metarterioles and arterioles. Only the microvascular smooth muscle cells loaded with fura-2 AM and changes in the fluorescence signal were confined to these cells: Endothelial cells did not make any contribution to the fluorescence signal nor did they contribute to the actions of the drugs. Caffeine (10 mM) or elevated K(+) (100 mM) produced a transient rise in cell Ca(2+) in the larger vessels (diameters >18 microm) but had no effect on smaller vessels (diameters <18 microm). Rises in cell Ca(2+) were accompanied by a rapid ( approximately 2 s to peak) contraction followed by relaxation. Caffeine and K(+) responses were blocked by ryanodine (10 microM) and nifedipine (1 microM), respectively. In all the vessels tested, vasopressin (arginine, 10 nM) elicited a transient increase in cell Ca(2+) and a constriction, irrespective of the diameter of the vessel. All vessels tested also responded to endothelin-1 (1-10 nM) through an Et(A) receptor to produce a transient rise in cell Ca(2+) followed by a plateau phase of elevated Ca(2+) and a constriction. In contrast to the transient effects of vasopressin, caffeine, and K(+), the cell Ca(2+) remained elevated (>30 min) on washing out the endothelin and the vessel failed to relax. These results demonstrate heterogeneity between smaller and larger retinal vessels with regard to Ca(2+) mobilisation and homogeneity with respect to the actions of vasoactive peptides.
Scholfield
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Smooth muscle group, Department of Physiology, Queens University, 97, Lisburn Road, Belfast, BT9 7BL, United Kingdom. N.SCHOLFIELD@QUB.AC.UK
Curtis
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TM
D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology; D001160:Arterioles / Q000378:metabolism; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism; D005260:Female; D017136:Ion Transport; D008297:Male; D008833:Microcirculation; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D044022:Receptor, Endothelin A; D017466:Receptors, Endothelin / Q000187:drug effects; D012161:Retinal Artery / Q000378:metabolism*; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism
D020746:Calcium Channels, L-Type; D044022:Receptor, Endothelin A; D017466:Receptors, Endothelin; D019837:Ryanodine Receptor Calcium Release Channel; D001127:Arginine Vasopressin; D012433:Ryanodine; D002110:Caffeine; D011188:Potassium; D002118:Calcium