Purinoceptor subtypes mediating contraction and relaxation of marmoset urinary bladder smooth muscle.
1. The effects of adenosine triphosphate (ATP), adenosine diphosphate (ADP), alpha,beta-methylene-ATP (alpha,beta-MeATP) and 2-methylthio-ATP (2-MeSATP) on longitudinally orientated smooth muscle strips from marmoset urinary bladder were investigated by use of standard organ bath techniques. 2. After being mounted in superfusion organ baths, 66.7% (n=249) of marmoset detrusor smooth muscle strips developed spontaneous tone, 48.2% of all strips examined developed tone equivalent to greater than 0.1 g mg(-1) of tissue and were subsequently utilized in the present investigation. 3. On exposure to ATP, muscle strips exhibited a biphasic response, a rapid and transient contraction followed by a more prolonged relaxation. Both responses were found to be concentration-dependent. ADP and 2-MeSATP elicited a similar response (contraction followed by relaxation), whereas application of alpha,beta-MeATP only produced a contraction. The potency order for each effect was alpha,beta-MeATP> >2-MeSATP> ATP>ADP (contractile response) and ATP=2-MeSATP> or = ADP> > alpha,beta-MeATP (relaxational response). 4. Desensitization with alpha,beta-MeATP (10 microM) abolished the contractile phase of the response to ATP, but had no effect on the level of relaxation evoked by this agonist. On the other hand, the G-protein inactivator, GDPbetaS (100 microM) abolished only the relaxation response to ATP. Suramin (general P2 antagonist, 100 microM) shifted both the contractile and relaxation ATP concentration-response curves to the right, whereas cibacron blue (P2Y antagonist, 10 microM) only antagonized the relaxation response to ATP. In contrast, the adenosine receptor antagonist, 8-phenyltheophylline (10 microM), had no effect on the relaxation response curve to ATP. 5. Incubation with tetrodotoxin (TTX, 3 microM) or depolarization of the muscle strip with 40 mM K+ Krebs failed to abolish the relaxation to ATP. In addition, neither Nomega-nitro-L-arginine (L-NOARG, 10 microM) nor methylene blue (10 microM) had any effect on the relaxation response curve. However, tos-phe-chloromethylketone (TPCK, 3 microM), an inhibitor of cyclicAMP-dependent protein kinase A (PKA), significantly (P<0.01) shifted the curve for the ATP-induced relaxation to the right. 6. It is proposed that marmoset detrusor smooth muscle contains two receptors for ATP, a classical P2X-type receptor mediating smooth muscle contraction, and a P2Y (G-protein linked) receptor mediating smooth muscle relaxation. The results also indicate that the ATP-evoked relaxation may occur through the activation of cyclicAMP-dependent PKA.
McMurray
G
G
University Department of Pharmacology, Oxford.
Dass
N
N
Brading
A F
AF
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002144:Callithrix; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D011983:Receptors, Purinergic / Q000187:drug effects*; D018047:Receptors, Purinergic P1 / Q000187:drug effects; D018048:Receptors, Purinergic P2 / Q000187:drug effects; D001743:Urinary Bladder / Q000187:drug effects / Q000294:innervation / Q000502:physiology*
D011983:Receptors, Purinergic; D018047:Receptors, Purinergic P1; D018048:Receptors, Purinergic P2; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate