Potentiation of Na+-electrogenic pump of airway smooth muscle by sensitization

Abstract

Camm-Hartley male guinea pigs were sensitized and then after a 14-day immunization period, resensitization was carried out. Resting membrane potential (Em) of airway smooth muscle (ASM) was determined with glass micro-electrodes. Simultaneously with Em the isometric force (IF) developed by the tracheal preparations was also determined. Measurements of both Em and IF were made before, during and after administration of histamine (10(-3) or 10(-5) M), ouabain (10(-5) M), K+-free solution and albumin (1%). It was found: (1) Sensitization and resensitization caused a significant hyperpolarization of airway smooth muscle cells. Em of ASM was -78.1 +/- 0.5 mV after the 3rd resensitization as compared with -61.3 +/- 0.5 mV in controls (P less than 0.001); (2) Tracheal preparations from resensitized animals had a greater response to histamine (10(-3) M or 10(-5) M). After histamine administration, both maximum contractile isometric force and the magnitude of maximal depolarization of airway smooth muscle preparations from resensitized animals (after the 2nd and 3rd resensitization) were higher (P less than 0.01) than similar responses seen in controls; (3) After albumin (1%), tissue from resensitized animals showed higher responses (P less than 0.01) than those from sensitized animals as measured by both isometric force and degree of depolarization; (4) Responses to ouabain (10(-5) M) and K+-free solution suggested that the Na+-electrogenic pump was potentiated in ASM from both sensitized and resensitized animals. It is concluded that sensitization and resensitization of guinea pigs may directly alter airway smooth muscle cell membrane function. Both sensitization and resensitization caused a potentiation of the electrogenic sodium pump in airway smooth muscle cells.