Alpha1A-adrenoceptor mediated contraction of rat prostatic vas deferens and the involvement of ryanodine stores and Ca2+ influx stimulated by diacylglycerol and PKC.
1 The present study has investigated the alpha1-adrenoceptor subtype mediating contraction of the rat isolated prostatic vas deferens and the possible effector mechanisms involved in this response by use of functional experiments. 2 Contractions to noradrenaline in the rat isolated prostatic vas deferens were antagonized by prazosin (9.4, 1.04+/-0.19, pA2 and Schild plot slope), 5-methyl urapidil (8.9, 1.10+/-0.13), BMY 7378 (6.4, 1.53+/-0.07) and RS 17053 (8.3, 1.13+/-0.18). These affinities are consistent with the response being mediated by the alpha1A-adrenoceptor subtype. 3 The contraction to noradrenaline at 37 degrees C consisted of an initial phasic response, composed of many rhythmic contractile spikes and a more slowly developing tonic contraction. When the temperature was lowered to 25 degrees C the phasic contraction became a smooth single response which was increased in magnitude. 4 In Ca2+-free Krebs solution the tonic contraction to noradrenaline (10(-4) M) was abolished, suggesting that this response was dependent on influx of extracellular Ca2+. After 2 min in Ca2+-free Krebs solution at 37 degrees C and 25 degrees C the phasic response to noradrenaline (10(-4) M) was 38+/-2% and 91+/-4%, respectively, compared with the phasic contraction to noradrenaline (10(-4) M in normal Krebs solution) and after 30 min it was abolished at 37 degrees C and was 7+/-1% at 25 degrees C. Ryanodine abolished the noradrenaline response in Ca2+-free Krebs solution for 2 min at 25 degrees C, while cyclopiazonic acid reduced it to 36+/-2%. 5 In normal Krebs solution at 25 degrees C the protein kinase C inhibitor calphostin C reduced the tonic contraction to noradrenaline (10(-5) M) from 36+/-8% to 14+/-3% compared with the phasic contraction to noradrenaline (10(-4) M). The DAG kinase inhibitor R 59022 increased the contraction following the initial phasic response to a maximum of 107+/-17% after 35 s, before dropping down to a well maintained contraction which was still greater in magnitude compared with the control. Nifedipine (3x10(-7) M) reduced the tonic contraction from 49+/-6% to 7+/-1% but did not reduce the phasic response. Ryanodine (10(-4) M) reduced the phasic contraction from 50+/-2% to 7+/-1% and the tonic response from 47+/-5% to 27+/-5%. 6 The phorbol ester phorbol-12,13-dibutyrate at 25 degrees C produced a transient contraction of the rat prostatic vas deferens, maximum response (10(-5) M) 48+/-4%, compared with the maximum tonic response to noradrenaline. The contraction to PDBu (10(-5) M) was reduced to 23+/-2% by calphostin C (10(-6) M) and to 15+/-1% by nifedipine (3x10(-7) M) and was abolished after 2 min in Ca2+-free Krebs solution. 7 In conclusion, the alpha1A-adrenoceptor mediated contraction to noradrenaline of the rat prostatic vas deferens appears to consist of an initial phasic component due to the release of intracellular Ca2+ from ryanodine-sensitive stores. These stores are depleted in the absence of extracellular Ca2+ and this depletion is slower at 25 degrees C than at 37 degrees C. The phasic contraction is followed by a tonic contraction involving activation of protein kinase C by diacylglycerol and influx of Ca2+ through nifedipine-sensitive channels.
Burt
R P
RP
Department of Pharmacology, University College London.
Chapple
C R
CR
Marshall
I
I
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004075:Diglycerides / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D009638:Norepinephrine / Q000494:pharmacology; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011467:Prostate / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure*; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects / Q000502:physiology*; D012433:Ryanodine / Q000378:metabolism / Q000494:pharmacology*; D013268:Stimulation, Chemical; D014649:Vas Deferens / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure*
C547715:Adra1a protein, rat; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D004075:Diglycerides; D018340:Receptors, Adrenergic, alpha-1; D012433:Ryanodine; D015240:Phorbol 12,13-Dibutyrate; D011493:Protein Kinase C; D002118:Calcium; D009638:Norepinephrine; D011224:Prazosin