Effects of acetylcholine, isoprenaline, phenylephrine and dibutyryl-cAMP on the contractility of isolated myocytes of the rat heart ventricles.
Single ventricular myocytes were isolated by enzymatic dissociation from the rat heart. The myocytes showed two types of spontaneous contractions: action potential dependent 'electric' contractions which occurred as short bursts, and slowly propagating contraction waves, i.e. phasic contractions. Electric contractions were normally found only in some of the myocytes, but in about 85% of the cells these could be induced by isoprenaline (ISO), phenylephrine (PHE), dibutyryl-cAMP (DB-cAMP) or acetylcholine (ACh). The inducing potency of the drugs was ACh greater than PHE greater than ISO greater than DB-cAMP. When electric contractions were blocked with verapamil, the frequency of phasic contractions was increased by ISO and DB-cAMP, whereas PHE and ACh had not this effect. In 45 min, ISO increased the frequency tenfold. High concentrations (10(-4) and 10(-5) M) of ISO lead to steady contracture of the myocytes in about 40% of the cells. The effect of DB-cAMP was weaker being only about 20% of that of ISO and it never caused steady contractures. The results suggest that alpha receptor activation by PHE does not affect the intracellular calcium movements but that ISO through beta receptor activation and DB-cAMP directly may increase the rate of calcium accumulation by sarcoplasmic reticulum (SR).
D000109:Acetylcholine / Q000494:pharmacology*; D000200:Action Potentials; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology*; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D010656:Phenylephrine / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
D010656:Phenylephrine; D003994:Bucladesine; D007545:Isoproterenol; D000109:Acetylcholine