Endothelin activates voltage-dependent Ca2+ current by a G protein-dependent mechanism in rabbit cardiac myocytes

J Physiol. 1992 Mar;448:729-47. doi: 10.1113/jphysiol.1992.sp019067.

Abstract

1. Endothelin is a vasoactive peptide released from vascular endothelial cells which has potent cardiac inotropic effects. We examined the effect of endothelin on the verapamil-sensitive Ca2+ current (ICa) in enzymatically dispersed rabbit ventricular myocytes. 2. Using the whole-cell voltage clamp technique with a standard dialysing pipette solution, the application of extracellular endothelin (20 nM) did not increase the peak ICa, but in fact caused a small reversible decline (903 +/- 109 pA without endothelin, 727 +/- 95 pA with endothelin (means +/- S.E.M., n = 14, P less than 0.05)). 3. If GTP (100 microM) was added to the pipette solution, the extracellular application of endothelin (0.2 or 20 nM) caused a large, reproducible increase in peak ICa (871 +/- 85 pA without endothelin, 1230 +/- 110 pA with 20 nM-endothelin (n = 10, P less than 0.05). The endothelin enhancement of ICa occurred after a delay of approximately 3-4 min at room temperature. 4. The GTP requirement for the endothelin effect on ICa suggests that its effect may be mediated through a G protein-dependent pathway. To investigate this further, experiments were performed with pipette solutions containing guanosine-5'-O-(2-thiodiphosphate) (GDP beta S), a GDP analogue which inhibits G protein cycling. With the addition of GDP beta S (0.5-5.0 mM) to the pipette solution (along with 100 microM-GTP), the effect of endothelin on peak ICa was blocked (1062 +/- 86 pA without endothelin, 1170 +/- 134 pA with endothelin (n = 11, P greater than 0.05)). 5. Incubation of myocytes with pertussis toxin (500 ng/ml) prevented the partial ACh-induced reversal of the isoprenolol enhancement of ICa. However, this identical treatment failed to block the endothelin enhancement of the voltage-dependent Ca2+ current (n = 4). 6. Taken together, these results confirm that while the effect of endothelin in rabbit cardiac ventricular myocytes is mediated through a G protein-dependent pathway, the G protein involved is pertussis toxin-insensitive.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acetylcholine / pharmacology
  • Animals
  • Calcium / metabolism*
  • Endothelins / pharmacology*
  • GTP-Binding Proteins / metabolism*
  • Guanosine Diphosphate / analogs & derivatives
  • Guanosine Diphosphate / pharmacology
  • Guanosine Triphosphate / pharmacology
  • In Vitro Techniques
  • Isoproterenol / pharmacology
  • Membrane Potentials / drug effects
  • Myocardium / metabolism*
  • Pertussis Toxin
  • Rabbits
  • Thionucleotides / pharmacology
  • Time Factors
  • Virulence Factors, Bordetella / pharmacology

Substances

  • Endothelins
  • Thionucleotides
  • Virulence Factors, Bordetella
  • Guanosine Diphosphate
  • guanosine 5'-O-(2-thiodiphosphate)
  • Guanosine Triphosphate
  • Pertussis Toxin
  • GTP-Binding Proteins
  • Isoproterenol
  • Acetylcholine
  • Calcium