The involvement of protein kinase C and tyrosine kinase in vanadate-induced contraction

Mechanisms underlying pervanadate-induced contraction of rat cremaster muscle arterioles

The current study examined the role of extracellular Ca2+, calmodulin and myosin light-chain kinase (MLCK) in pervanadate-induced constriction of cannulated, pressurized rat cremaster arterioles. Pervanadate (0.03-100 microM) induced a concentration-dependent constriction of arterioles that was significantly attenuated (P<0.05) by the tyrosine kinase inhibitor tyrphostin 47 (30 microM). The L-type voltage-sensitive Ca2+ channel antagonists verapamil (10 microM) and nifedipine (1 microM) dilated vessels possessing myogenic tone but had no demonstrable effect on pervanadate constriction, while a higher concentration of nifedipine (10 microM) reduced constriction by approximately 50%. Pervanadate-induced contractions were reduced by the calmodulin inhibitor W-7 (N-(6-aminohexyl)-chloro-1-naphtalene sulphonamide, 50 microM) and the MLCK inhibitor ML-7 (1-(5-iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine, 10 or 30 microM). Removal of extracellular Ca2+ abolished the contractile effect of pervanadate. Measurement of changes in arteriolar wall [Ca2+] using the Ca2+ sensitive dye Fura-2 showed that pervanadate did not increase [Ca2+] during arteriolar constriction. These observations suggest that pervanadate-induced contraction of smooth muscle in the cremaster arteriole involves Ca2+/calmodulin-dependent myosin phosphorylation and possibly sensitization of the contractile apparatus to Ca2+.

Smooth muscle in the annulus fibrosus of the tympanic membrane: physiological effects on sound transmission in the gerbil

In a wide variety of mammals, the rim of the tympanic membrane (annulus fibrosus) has an array of contractile elements, either smooth muscle [Henson and Henson, J. Assoc. Res. Otolaryngol. 1 (2000) 25-32] or myofibroblasts [Kuijpers et al., Hear. Res. 128 (1999) 80-88]. These elements are anchored peripherally to the bony tympanic ring and centrally to incoming fibers of the pars tensa. Their arrangement suggests that they are involved in the control of tympanic membrane tension. In this study, cochlear microphonic (CM) threshold changes were recorded in gerbils to study the physiological effects of these contractile elements. It was demonstrated that the application of substances known to make smooth muscle contract (vanadate and norepinephrine) caused concentration-dependent elevations in CM thresholds. Maximum changes of 8-9 dB occurred with the lowest frequency tested (2.16 kHz). The application of muscle-relaxing drugs reversed these effects. Controls showed that the threshold changes were not induced by effects on middle or inner ear structures. These results add to emerging evidence that the tympanic membrane has intrinsic control of tension and is potentially able to have some control over energy levels reaching the cochlea.