Two threonine residues in the M2 segment of the α1β1 GABA(A) receptor are critical for ion channel function.

Abstract

The role of three threonine residues in the M2 hydrophobic region of the GABA(A) receptor has been investigated by replacing these polar residues with alanine at the 6', 10' or 13' positions of M2 in the GABA(A) α1 and β1 subunits and co-expressing the mutated subunits in the baculovirus Sf9 insect cell system. GABA did not elicit a current in cells expressing either the 6' or 13' threonine to alanine mutants. The mutant subunits formed intact heteromeric GABA(A) receptors as judged by the binding of [3H] muscimol or the relative level of α1 protein present in the plasma membrane. In contrast, a chloride current was generated by GABA in cells expressing the 10' mutant receptor. However, the current decayed more rapidly to baseline in the continued presence of GABA in the 10' mutant receptor than in the wild type receptor. The results are discussed in terms of the possible roles of the threonine residues in the ion conduction pathway. Show more