Mechanisms underlying spontaneous rhythmical contractions in irideal arterioles of the rat.
1. Mechanisms underlying spontaneous rhythmical contractions have been studied in irideal arterioles of the rat using video microscopy and electrophysiology. 2. Rhythmical contractions (4 min-1) were more common during the second and third postnatal weeks and were always preceded by large, slow depolarizations (5-40 mV). 3. Spontaneous contractions were unaffected by tetrodotoxin (1 microM), neurotransmitter receptor antagonists, the sympathetic neurone blocker, guanethidine (5 microM) or sensory neurotoxin, capsaicin (1 microM). 4. Stimulation of sensory nerves inhibited spontaneous activity and this was not prevented by L-NAME (10 microm). 5. L-NAME (10 microm) caused an increase in frequency of spontaneous contractions, while forskolin (30 nM), in the presence of L-NAME, abolished spontaneous, but not nerve-mediated, contractions. 6. Spontaneous activity was not affected by felodipine (1 nM) or nifedipine (1 microM), but was abolished by cadmium chloride (1 microM) or superfusion with calcium-free solution. 7. Caffeine (1 mM), thapsigargin (2 microM) and cyclopiazonic acid (3 microM), but not ryanodine (3 microM), abolished spontaneous and nerve-mediated contractions. After preincubation in L-NAME (10 microM), cyclopiazonic acid abolished spontaneous contractions only. 8. Spontaneous depolarizations and contractions were abolished by 18alpha-glycyrrhetinic acid (20 microM). 9. Results suggest that spontaneous rhythmical contractions are myogenic and result from the cyclical release of calcium from intracellular stores, without a contribution from voltage-dependent calcium channels. Intercellular coupling through gap junctions appears to be essential for co-ordination of these events which could be modulated by nitric oxide and increases in cAMP. The possibility that different intracellular stores underly spontaneous and nerve-mediated contractions is discussed.
Hill
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Division of Neuroscience, John Curtin School of Medical Research, Australian National University, GPO Box 334, Canberra, ACT 2601, Australia. caryl.hill@anu.edu.au
Eade
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Sandow
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D000255:Adenosine Triphosphate / Q000494:pharmacology; D000367:Age Factors; D000818:Animals; D001160:Arterioles / Q000502:physiology; D019256:Cadmium Chloride / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002211:Capsaicin / Q000494:pharmacology; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D015226:Dinucleoside Phosphates / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015736:Felodipine / Q000494:pharmacology; D005260:Female; D017629:Gap Junctions / Q000502:physiology; D007498:Iris / Q000098:blood supply*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009478:Neuropeptide Y / Q000037:antagonists & inhibitors / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology; D010507:Periodicity; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012433:Ryanodine / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D014661:Vasoconstriction / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology
C097287:1229U91; D000697:Central Nervous System Stimulants; D015226:Dinucleoside Phosphates; D004791:Enzyme Inhibitors; D009478:Neuropeptide Y; D010456:Peptides, Cyclic; D010975:Platelet Aggregation Inhibitors; D014665:Vasodilator Agents; C077792:pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid; D012433:Ryanodine; D005576:Colforsin; C013907:cytidylyl adenosine; D002110:Caffeine; D011732:Pyridoxal Phosphate; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D019256:Cadmium Chloride; D015736:Felodipine; D002211:Capsaicin; D002118:Calcium; D019331:NG-Nitroarginine Methyl Ester