Sites and modes of action of proctolin and the FLP F2 on lobster cardiac muscle.

Abstract

At the threshold concentration (1-10 pmol l(-1)), the neuropeptide hormones proctolin (PR) and the FLRFamide-like peptide (FLP) F(2) cause an increase in amplitude of electrically evoked contractions (each contraction is a brief tetanus) of lobster heart ostial muscle. At higher concentrations each peptide also induces an increase in tonus (contracture). The PR-induced contracture and augmentation of tetani are proportional to increases in [Ca2+]i. The rate of onset and recovery of peptide-induced effects on both tetani and contracture appeared to reduced by Ca2+ storage by the sarcoplasmic reticulum (SR). Enhanced tetani following a contracture may be due to enhanced voltage-gated Ca2+ current and sarcoplasmic reticular (SR) Ca2+ loading. The SR Ca2+ loading appears to be specific for PR and F2, since glutamic-acid-induced contractures are not followed by increased tetani. The prolonged elevation of [Ca2+]i during contracture causes a right-ward shift in the force-pCa curve indicating a decrease in myofibrillar sensitivity to Ca2+. Blocking voltage-gated Ca2+ channels with Cd2+, nifedipine or verapamil, while reducing tetani, does not prevent peptide-induced contracture and enhanced tetani. Opening SR Ca2+ channels and depleting SR Ca2+ with either caffeine or ryanodine blocked tetani but permitted accelerated peptide-induced contractures. We conclude that PR and F2 at low concentration enhance voltage-dependent Ca2+ induced Ca2+ release from the SR, while higher hormone levels directly gate Ca2+ entry across the sarcolemma.

• Authors: J L Wilkens, T Shinozaki, T Yazawa, H E D J ter Keurs
• Journal: The Journal of experimental biology (J Exp Biol) Vol. 208 Issue Pt 4 Pg. 737-47 (Feb 2005) ISSN: 0022-0949 [Print] England
• PMID: 15695765 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Calcium Channel Blockers
• Calcium Channels
• Neuropeptides
• Oligopeptides
• Cadmium
• Ryanodine
• Caffeine
• proctolin
• phenylalanyl-leucyl-arginyl phenylalaninamide
• Verapamil
• Nifedipine
• Calcium

Topics

• Animals
• Cadmium (metabolism)
• Caffeine (metabolism)
• Calcium (metabolism)
• Calcium Channel Blockers (metabolism)
• Calcium Channels (metabolism)
• Fluorescence
• Membrane Potentials
• Microelectrodes
• Myocardial Contraction (drug effects)
• Myocardium (metabolism)
• Nephropidae (metabolism)
• Neuropeptides (metabolism, pharmacology)
• Nifedipine (metabolism)
• Oligopeptides (metabolism, pharmacology)
• Ryanodine (metabolism)
• Sarcoplasmic Reticulum (drug effects, metabolism)
• Verapamil (metabolism)