Exocytosis elicited by ACh was increased by varenicline, nicotine and by both drugs together in rat chromaffin cells treated chronically with nicotine
In a different set of experiments, chromaffin cells from six rats were incubated with 110 nM nicotine for 24 hours and then perfused during the whole experiment. The same protocol as in Fig. 1 was performed. Representative original Cm traces are drawn in Fig. 4A-D for control conditions, and in the presence of varenicline, nicotine and both drugs applied together, respectively. The exocytosis achieved in control cells amounted to 58.2 ± 6.1 fF (n=8). Varenicline alone evoked 120.7 ± 20.7 fF (n=6, *p) and nicotine triggered 160.9 ± 28.5 fF (n=6, *p). Varenicline and nicotine elicited 186.5 ± 32.3 fF (n=8, *p). The average values of Cm are displayed in Fig. 4E and the normalized values with respect to its own control are shown in Fig. 4F. Varenicline alone exhibited an increase in the exocytotic value of 2.4 ± 0.5 fold (n=6; *p), and nicotine triggered 3.1 ± 0.6 fold more exocytosis with respect to control (n=6; *p). The response elicited by varenicline together with nicotine was 3.4 ± 0.7 fold with respect to the control response (n=8; *p). Thus, exocytotic responses were also increased by varenicline alone or in the presence of nicotine, when the chronic nicotine treatment was applied.
The values achieved for the membrane potential in these cells were -62.2 ±1.3 mV (n=8), -57.8 ± 7.5 mV (n=6), -55.2 ± 3.4 mV (n=6) and -51.5 ± 2.6 mV (n=8, *p), for control conditions, varenicline and nicotine alone, and both drugs perfused together, respectively. This reflects that nicotine, in the acute and chronic treatment, may depolarize the cell membrane in the presence of varenicline.