Regulation of L- and N-types of Ca2+ channels by intracellular ATP4- in frog dorsal root ganglion neurons.
The roles of free Mg2+ ions, ATP4- ions and Mg-ATP complexes in the regulation of N- and L-types of Ca2+ channels were studied in frog dorsal root ganglion (DRG) neurons using the whole-cell patch-clamp technique. Because Mg2+ ions interact with ATP4- ions to form Mg-ATP complexes, addition of one species can influence the concentrations of the other two. In this study their concentrations were carefully controlled by varying the concentrations of two constituents at a time while keeping the third constant. The effects of each of the three species on barium currents through L-type (IBaL) and N-type (IBaN) Ca2+ channels were plotted against its concentrations. The dose-response curves for ATP4- show that IBaL and IBaN proportionally increased with ATP4- concentrations up to 1 mM at three different Mg2+ concentrations. At a fixed concentration of ATP4-, IBaL and IBaN remained unchanged even when pMg changed from 3 to 5. Dose-response curves for IBaL and IBaN plotted against Mg-ATP concentration did not show a consistent pattern. H-7 and Mg2+ ions did not exert any blocking effect on the activity of either Ca2+ channel type, and neither dibutyryl-cAMP nor NKH-477 had any stimulating effect, suggesting that phosphorylation is not likely to be involved in ATP-induced potentiation. From these observations, it is concluded that L-type and N-type Ca2+ channels in frog DRG neurons are regulated by ATP4- ions alone, and that the neuronal Ca2+ channels are regulated by mechanisms that are different from those regulating the cardiac Ca2+ channels.
Yuki
T
T
Department of Physiology, School of Medicine, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, 734-8551, Japan.
Yamaoka
K
K
Seyama
I
I
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D001464:Barium / Q000378:metabolism; D003994:Bucladesine / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D020746:Calcium Channels, L-Type; D004594:Electrophysiology; D005727:Ganglia, Spinal / Q000502:physiology*; D066298:In Vitro Techniques; D008274:Magnesium / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011892:Rana catesbeiana
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D001464:Barium; D003994:Bucladesine; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000255:Adenosine Triphosphate; D008274:Magnesium