Mytilus inhibitory peptide (MIP) induces a Na+-activated K+-current in snail neurons.
Two microelectrode voltage-clamp and single-channel recordings were performed on D-cluster neurons of snail right parietal ganglion in order to study the properties of MIP-activated potassium current. It was found that the octapeptide member of the MIP-family, ASHIPRFVa elicits an outward current, which possesses all the properties characteristic for the hexapeptide(s) inward membrane response. The main component of the peptide elicited response is highly [K+]o dependent, however the response was attenuated in Na-free extracellular saline. The peptide elicited response was mimicked by raising the [Na+]i by pressure injection of Na+ into the cell. Single channel recordings indicated that MIP-induced outward K-current is Na-dependent. The probability to find a channel in open state increases with increasing intracellular Na+-concentration. Excised inside-out patches obtained from D-neurons contained I(K(Na)) channels could be activated by exposure of the cytoplasmic face of the patch membrane to 40 mM Na+, and 40 mM Li+, as well. The single channel current amplitude at -60 mV is 15 pA and the single channel conductance is 212 pS between -80 and 0 mV. It was concluded that MIP's activate a novel type of K+-current in the snail neurons. This current is the Na-activated K+-current. The single channel properties of the MIP activated channel is in concert with I(K(Na)) data obtained on different vertebrate and invertebrate preparations.
Kiss
T
T
Department of Experimental Zoology, Balaton Limnological Research Institute of the Hungarian Academy of Sciences, Tihany. kisst@tres.blki.hu
Fujisawa
Y
Y
László
Z
Z
Muneoka
Y
Y
D000595:Amino Acid Sequence; D000818:Animals; D049872:Bivalvia; D006372:Helix, Snails; D066298:In Vitro Techniques; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism*; D009479:Neuropeptides / Q000737:chemistry / Q000494:pharmacology*; D009842:Oligopeptides / Q000737:chemistry / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects* / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism
C055988:Mytilus inhibitory peptide; D009479:Neuropeptides; D009842:Oligopeptides; D015221:Potassium Channels; D012964:Sodium