Inositol hexakisphosphate excites rat medullary sympathoexcitatory neurons in vivo.
Inositol hexakisphosphate (IP6) was microinjected into the rostral ventrolateral reticular nucleus or iontophoresed onto reticulospinal sympathoexcitatory neurons of the nucleus in anesthetized rats. IP6 (5-500 pmol) induced a dose-dependent potent and prolonged elevation of arterial pressure which was mimicked by microinjection of ethyleneglycol-bis (beta-aminoethylether)N,N,N',N'-tetraacetic acid (EGTA), while myo-inositol was ineffective. Iontophoretic application of IP6 and EGTA excited the medullary sympathoexcitatory neurons but myo-inositol had no effect. The effect of IP6 on firing rate of the sympathoexcitatory neurons was abolished by co-administration of Ca2+ ions onto these neurons. The results indicate that IP6 acts extracellularly to excite the medullary sympathoexcitatory neurons. The excitatory actions of IP6 may depend, at least in part, on a calcium-chelating action. Chelation of extracellular Ca2+ might be a physiological action of IP6.
Sun
M K
MK
Department of Neurology and Neuroscience, Cornell University Medical College, New York, NY 10021.
Wahlestedt
C
C
Reis
D J
DJ
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002122:Calcium Chloride / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000494:pharmacology; D007294:Inositol / Q000494:pharmacology; D007478:Iontophoresis; D008297:Male; D008526:Medulla Oblongata / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D008845:Microinjections; D009046:Motor Neurons / Q000187:drug effects* / Q000502:physiology; D010833:Phytic Acid / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013564:Sympathetic Nervous System / Q000166:cytology / Q000187:drug effects* / Q000502:physiology
D002614:Chelating Agents; D007294:Inositol; D004533:Egtazic Acid; D010833:Phytic Acid; D002122:Calcium Chloride; D002118:Calcium