Exocytosis elicited by ACh was increased by varenicline,
nicotine or by both agonists together in rat chromaffin cells
The final goal of the use of rat chromaffin cells was to investigate
whether the chronic treatment of the cells with nicotine, that will
mimic the situation of a chronic smoker, will increase exocytosis. In a
latter step, we investigated whether the effects of these drugs on
exocytosis could be due to an effect on the nicotinic currents. First,
we investigated whether previous results obtained in Fig. 1 were
reproducible in rat chromaffin cells. We performed the same protocol
described in Fig. 1 in chromaffin cells of ten rats. Representative
recordings under the control condition, varenicline, nicotine or both
drugs together are shown in Fig. 3A-D, respectively. Exocytosis elicited
under control conditions amounted to 107.5 ± 30.1 fF (n=21). The same
protocol was tested with 100 nM varenicline or 250 nM nicotine,
eliciting 173.6 ± 40.6 fF (n=18) and 171.8 ± 49.2 fF (n=16) of
exocytosis respectively. Varenicline and nicotine evoked 196.5 ± 38.9 fF
(n=20, *p) of exocytosis. There was a period of 5 min wash-out between
the different treatments. Average values are shown in Fig. 3E.
In order to compare these responses and due to the high variability of
the control responses (from 24 fF to 466 fF), each result was compared
and normalized with its own control. Varenicline increased the response
to 2.2 ± 0.4 fold (n=18; *p) and nicotine increased it to 2.4 ± 0.6 fold
(n=16; *p). Both drugs perfused together increased by 2.9 ± 0.5 fold the
exocytotic response (n=20; *p) (Fig. 3F). There was no change in the
membrane potential when the different drugs were perfused during the
Step 2. Under control conditions, the membrane potential was -56.4 ±2 mV
(n=21), and it reached the values of -57.3 ± 2.7 mV (n=18), -57 ± 2.6 mV
(n=16) and -58 ± 2 mV (n=20) in the presence of varenicline, nicotine
and varenicline perfused together with nicotine, respectively.