The influence of hypothermia on P2 receptor-mediated responses of frog skeletal muscle.
The contractile responses of isolated Rana ridibunda frog sartorius muscle contractions evoked by electrical field stimulation (EFS) were studied at three temperature conditions of 17, 22 and 27 degrees C. Temperature-dependent increase of muscle contractility was found. ATP (10-100 microM) concentration dependently inhibited the electrical field stimulation-evoked contractions of sartorius muscle at all three temperatures; this effect was significantly more prominent at a temperature of 17 degrees C than at other two temperatures. Adenosine (100 microM) also caused inhibition of electrical field stimulation-evoked contractions which was statistically identical at all three temperature conditions tested. A P2 receptor antagonist, pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 10 microM) reduced the inhibitory effect of ATP at all three temperatures but did not affect inhibitory action of adenosine. In contrast, 8-(p-sulfophenyl)theophylline (8-SPT, 100 microM), a nonselective P1 receptor antagonist, abolished inhibitory effects of adenosine at all three temperature conditions but did not antagonize inhibition caused by ATP. In electrophysiological experiments, ATP (100 microM) and adenosine (100 microM) temperature dependently reduced end-plate currents recorded in sartorius neuromuscular junction by voltage-clamp technique. The inhibitory effects of both agonists were enhanced with the decrease of temperature. 8-SPT (100 microM) abolished the inhibitory effect of adenosine but not ATP on end-plate currents. Suramin (100 microM), a nonselective P2 receptor antagonist, inhibited the action of ATP but not adenosine, while PPADS (10 microM) had no influence on the effects of either ATP or adenosine. It is concluded from this study that the effectiveness of P2 receptor-mediated inhibition of frog skeletal muscle contraction in contrast to that of adenosine is dependent on the temperature conditions.
Ziganshin
Airat U
AU
Department of Pharmacology, Kazan State Medical University, 49 Butlerov Street, Kazan 420012, Russia. airatziganshin@yahoo.co.uk
Kamaliev
Rafis R
RR
Grishin
Sergey N
SN
Ziganshina
Lilia E
LE
Zefirov
Andrey L
AL
Burnstock
Geoffrey
G
D000200:Action Potentials / Q000187:drug effects; D000241:Adenosine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D011189:Potassium Chloride / Q000494:pharmacology; D058915:Purinergic P1 Receptor Antagonists; D058919:Purinergic P2 Receptor Antagonists; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D011895:Rana ridibunda; D018047:Receptors, Purinergic P1 / Q000502:physiology; D018048:Receptors, Purinergic P2 / Q000502:physiology*; D013498:Suramin / Q000494:pharmacology; D013696:Temperature; D013806:Theophylline / Q000031:analogs & derivatives* / Q000494:pharmacology
D058915:Purinergic P1 Receptor Antagonists; D058919:Purinergic P2 Receptor Antagonists; D018047:Receptors, Purinergic P1; D018048:Receptors, Purinergic P2; C077792:pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid; D011732:Pyridoxal Phosphate; D013498:Suramin; D011189:Potassium Chloride; C031433:8-(4-sulfophenyl)theophylline; D000255:Adenosine Triphosphate; D013806:Theophylline; D000241:Adenosine