Initiation of the Phosphoinositide Cycle by Parathyroid Hormone in Synaptosomes

D. N. Khudaverdyan,^1,2 A. S. Ter-Markosian,¹ and Yu. V. Tadevosyan³

¹Geratsi Yerevan State Medical University, ul. Koryuna 2, Yerevan, 375025 Republic of Armenia; fax: (852) 52-1791.

²To whom correspondence should be addressed.

³Institute of Molecular Biology, Armenian National Academy of Sciences, ul. Asratyana 7, Yerevan, 375044 Republic of Armenia.

Submitted May 8, 1997; revision submitted July 11, 1997.

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We studied the effects of parathyroid hormone (10^-9 M) on the contents of mono-, di-, and triglycerides, total phospholipids, and free arachidonic acid in rat brain cortex synaptosomes using [1-¹⁴C]arachidonic acid at 2, 5, and 10 sec after addition of the hormone. Our data demonstrated the changes in lipid metabolism in synaptosomal membranes which were especially pronounced at 5 sec after addition of parathyroid hormone. Incorporation of 70% of [1-¹⁴C]arachidonic acid into the phosphoinositide fraction and the progress of changes in lipid metabolite composition suggest that the phosphoinositide cycle is initiated by parathyroid hormone, and the hormonal signal may be subsequently mediated in nerve cells by 1,2-diacylglycerol, a product of the phosphoinositide cycle.

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KEY WORDS: synaptosomes, phospholipid, phosphoinositide cycle, parathyroid hormone, calcium.

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