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Pharmacology and thermosensitivity of the dartos muscle isolated from rat scrotum

Research output: Contribution to journalArticle

A Gibson, A Akinrinsola, T Patel, A Ray, J Tucker, I McFadzean

Original languageEnglish
Pages (from-to)1194 - 1200
Number of pages7
JournalBritish Journal of Pharmacology
Volume136
Issue number8
DOIs
Publication statusPublished - Aug 2002

King's Authors

Abstract

1 The dartos is a thin sheet of smooth muscle closely associated with the skin of the scrotum. Although known to play an important role in scrotal thermoregulation, there has been no detailed study into the pharmacology, or thermosensitivity, of the dartos from any species. Here, we investigate these two parameters in the isolated dartos muscle from rat. 2 Field stimulation of the rat dartos caused contractions that were abolished by tetrodotoxin, phentolamine and guanethidine, but unaffected by atropine or L-N-G-nitroarginine. Exogenous noradrenaline also produced contractions blocked by both phentolamine and prazosin. In muscles with raised tone and negated sympathetic function, field stimulation failed to elicit relaxation. The dartos muscle did not contract in response to carbachol, nicotine, histamine, 5-hydroxytryptamine (all up to 100 pm) or substance P (up to 1 muM. 3 Contractile responses to field stimulation and noradrenaline were much greater at 30degreesC compared with 40degreesC; indeed, contractions to 1 muM noradrenalme at 30degreesC were relaxed by around 80% on heating to 40degreesC. Similar heat-induced relaxations were observed during contractions to both U46619 (100 nM) and high K (70 mm). 4 In contrast, contractile responses to the myosin phosphatase inhibitor calyculin-A (1 muM), either in the presence or absence of external calcium, were resistant to relaxation by heating. In calcium-free medium at 30degreesC, U46619 continued to produce contractions that were again relaxed by 80% on heating to 40degreesC. However, in the presence of calyculin-A, this heat-induced relaxation was greatly reduced. 5 Thus, the rat dartos muscle receives a functional sympathetic innervation and contracts to noradrenaline via alpha-adrenoceptors. There is no functional inhibitory innervation. Experiments with calyculin-A suggest that myosin phosphatase is a major contributor to the marked thermosensitivity of the dartos muscle.

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