Plasma membrane events associated with the meiotic divisions in the amphibian oocyte: insights into the evolution of insulin transduction systems and cell signaling

Table 3 Effect of insulin on the plasma membrane potential of the denuded rana oocyte as a function of external Na ⁺ and inhibitors of Na ⁺ channels/Na ⁺ :H ⁺ exchange, Na ⁺ /K ⁺ -ATPase and serine protease activity

Medium	E_mVcontrol	E_mV10 μM insulin^a
Ringer’s Solution (114 mM Na⁺)	−42.6 ± 1.6 (8)^b	−59.2 ± 1.7 (8)
2.5 mM Na⁺-Ringer’s Solution	−75.0 ± 1.0 (10)	−69.0 ± 3.0 (5)
1.0 mM Amiloride/Ringer’s Solution	−68.7 ± 1.4 (7)	−69.0 ± 2.1 (5)
10 μM Strophanthidin/Ringer’s Solution	−26.4 ± 1.0 (10)	−45.7 ± 0.6 (10)^c
1 h pretreatment with 1.0 mM PMSF in Ringer’s Solution	−39.1 ± 1.5 (7)	−38.0 ± 1.5 (12)
1.0 mM PMSF added with insulin		−60.1 ± 3.2 (7)

^aMean ± SE 60–90 min after addition of insulin. “Instantaneous” conductance was 3.2 ± 0.5, 1.85 ± 0.4 and 1.30 ± 0.3 μS for untreated, insulin-treated and amiloride-treated oocytes, respectively.
^b Number of sibling oocytes.^c30-60 min after addition of 10 μM strophanthidin

ISSN: 1471-213X