Mechanical response to noradrenaline in calcium‐free solution in the rat vas deferens.

Abstract

SUMMARY1. Mechanical responses to noradrenaline (NA) were investigated in the rat vas deferens exposed to Ca-free solution containing 0.5 mM-EGTA. A tonic response was produced in Ca-free solution at the epididymal portion, while almost no response could be observed at the prostatic portion.2. In most experiments NA (10-4 M) was applied for 4 min, every 20 min. The absolute tension development in Ca-free solution was usually 60-80 %0 of the control tonic response in the presence of 2-4 mM-Ca. The response could be produced repeatedly, even after exposure to Ca-free solution for more than 20 hr, without a significant decrease. During the first hour of exposure to Ca-free solution, the rate of rise and the magnitude of the NA contraction increased and then remained constant, though the relaxation became slow. 3. Transient treatment with 2-4 mM-Ca slightly suppressed the subsequent NA response in Ca-free solution. Similarly, the NA response was smaller during readmission of 0-2-0{5 mM-Ca than that obtained before Ca readmission.4. A high concentration of verapamil (2 x 10-4 M) reversibly reduced the NA response by about 700 after 30 min. Theophylline (10 mM) and dibutyryl cyclic AMP (10-4 M) also reversibly suppressed the NA response, the suppression being about 800%. None of these substances produced a tension change by themselves. The suppressing effect may be mediated via an increase of intracellular cyclic AMP which reduces phosphorylation of myosin. Caffeine (10 mM) and dibutyryl cyclic GMP (10-4 M) had similar but much weaker effects than theophylline and dibutyryl cyclic AMP.5. A calmodulin antagonist, N-(6-aminohexyl)-5-chloro-1 -naphthalene sulphonamide (W-7) slowly reduced the NA response. The block was nearly complete after 30 min treatment with 3 x 10-4 M-W-7, and the recovery was very poor after prolonged exposure. This effect of W-7, which is the same in the presence and absence of Ca, suggests that a Ca-calmodulin reaction is involved in the NA response in Ca-free solution.6. Fluoride at a concentration higher than 3 mm increased the muscle tone in the absence of external Ca, and transiently potentiated the NA response. In the presence of F-, the relaxation of the NA response was incomplete and the muscle tone increased stepwise after each NA application. When the muscle tone became higher than the F. ASHOORI AND T. TOMITA NA response in the absence of F-, the NA response was abolished. The action of several metabolic inhibitors (2,4-dinitrophenol carbonylcyanide chlorophenyl hydrazone, NaCN, monoiodoacetate) was similar to that of F-, suggesting that they release Ca from mitochondria, causing tension development.7. The observations are consistent with the hypothesis that the contraction of the vas deferens caused by NA in the absence of external Ca depends on the availability of intracellular Ca, stored in mitochondria and released by NA.

Calcium modulatory properties of 2,6‐dibutylbenzylamine (B25) in rat isolated vas deferens, cardiac and smooth muscle preparations

“…The rhythmic activity induced in the rat vas deferens by B25 appeared to be very similar to the contractile effect obtained in this preparation with different compounds (Hay & Wadsworth, 1979;Ashoori & Tomita, 1983;Mishra et al, 1988). In these reports the effects of some procedures affecting calcium translocation indicate that rhythmic contractions were highly dependent upon the activation of VSCC in the membrane.…”

“…Regardless of what agonist has been used, this rhythmic activity has proved to be closely dependent upon external calcium since it was completely prevented in CaCl2-free Krebs solutions (Ashoori & Tomita, 1983;Hay & Wadsworth, 1979;. More recently Langton & Huddard (1987) have shown that in the rat vas deferens, the rhythmic activity induced by slight depolarizing KCI solutions could be selectively mediated by rapidly inactivating voltage-sensitive calcium channels (VSCC) in the membrane.…”

Maintained contractions of rat uterine smooth muscle incubated in a Ca2+‐free solution

“…It has been proposed that, during maintained contractions, Ca2+ is mobilized by neurotransmitters from an intracellular pool which may be different from that responsible for the initial transient contraction (Heaslip & Rahwan, 1982;Ashoori & Tomita, 1983) whereas Casteels et al, (1981) envisaged the possibility that noradrenaline could also affect the contractile proteins by a mechanism which does not include a change in cytoplasmic Ca2+ concentration.…”

Effects of cytochalasins on the mechanical and membrane responses in the isolated longitudinal myometrium of pregnant rat with reference to the EGTA-resistant contraction.

“…In respect to the latter, it may be stressed that the amplitude of agonist-induced contractions increases progressively by prolonged exposure to Ca-free solution for longer than 20 h in the cases of vas deferens (ASHOORI and ToMITA , 1983), rat myometrium (ASHOORI et al, 1985), and guinea pig stomach (ASHOORI et al ., 1986). Progressive increase of the ATP-induced contraction due to prolonged exposure to Ca-free solution is also indicated in the present experiment (Figs .…”

“…EGTA-resistant contraction. Contractions can be evoked in Ca-free media in various smooth muscle tissues including blood vessels, vas deferens , and stomach (DETH and VAN BREEMEN, 1977;CASTEELS et al, 1981;ASHOORI and TOMITA, 1983;ITOH et al, 1983;BOND et al, 1984;AsxooRl et al, 1986), when agonists are applied . Such contractions are also shown to occur in myometrial smooth muscle (see introduction for references).…”