G protein-mediated FMRFamidergic modulation of calcium influx in dissociated heart muscle cells from squid, Loligo forbesii

• Published in: The Journal of physiology Vol. 525; no. 2; pp. 471 - 482
• Main Authors: Chrachri, Abdesslam, Ödblom, Maria, Williamson, Roddy
• Format: Journal Article
• Language: English
• Published: Oxford, UK The Physiological Society 01.06.2000; Blackwell Science Ltd; Blackwell Science Inc
• Subjects: Animals; Calcium - metabolism; Calcium Channels, L-Type - drug effects; Calcium Channels, L-Type - metabolism; Calcium Channels, T-Type - drug effects; Calcium Channels, T-Type - metabolism; Cell Separation; Decapodiformes - cytology; Decapodiformes - metabolism; FMRFamide - pharmacology; GTP-Binding Proteins - metabolism; Guanosine 5'-O-(3-Thiotriphosphate) - pharmacology; Guanosine Diphosphate - analogs & derivatives; Guanosine Diphosphate - pharmacology; In Vitro Techniques; Kinetics; Loligo forbesii; Membrane Potentials; Myocardium - cytology; Myocardium - metabolism; Original; Pertussis Toxin; Thionucleotides - pharmacology; Virulence Factors, Bordetella - pharmacology
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1111/j.1469-7793.2000.00471.x

The actions of the neuropeptide FMRFamide (Phe-Met-Arg-Phe-NH 2 ) on the L-type ( I Ca,L ) and T-type ( I Ca,T ) calcium currents were investigated in muscle cells dissociated from the heart of squid, Loligo forbseii . The heart muscle cells could be divided into type I and type II cells, on the basis of morphological differences in the dissociated myocytes. FMRFamide induced a substantial block of the L-type calcium current seen in type I cells; this inhibition was rapid, reversible and dose dependent (IC 50 = 0.1 μ m ). FMRFamide induced an increase in the amplitude of the L-type calcium current in the type II heart muscle cells, but had no effect on the T-type calcium current in either type of dissociated heart muscle cell, even at concentrations much higher than those found to affect the L-type calcium current. Internal dialysis of isolated type I heart muscle cells with guanosine 5′- O -(3-thiotriphosphate (GTPγS, 100 μ m ), a non-hydrolysable GTP analogue, mimicked the FMRFamide inhibition of the Ca 2+ current and occluded any further FMRFamide-induced inhibition. Internal dialysis of these cells with guanosine 5′- O -(2-thiodiphosphate) (GDPβS, 100 μ m ) reduced the FMRFamide-induced inhibition of the peak Ca 2+ current. The inhibitory effects of FMRFamide were abolished by pre-incubation of the cells with pertussis toxin (200 ng ml −1 ). The activation kinetics of I Ca,L were not affected by FMRFamide application, nor by internal perfusion with GTPγS, and the FMRFamide-induced reduction in I Ca,L was not relieved by large depolarising prepulses. These data indicate that FMRFamide can modulate I Ca,L , but not I Ca,T , in squid heart muscle cells, and that the underlying G protein pathway is dissimilar to that commonly associated with transmitter modulation of channel activity. The FMRFamide-modulated increase in I Ca,L seen in the type II heart muscle cells was not mediated by a PTX-sensitive G protein pathway.