SUMMARY1. Acetylcholine-induced currents recorded from bovine adrenal medullary chromaffin cells maintained in culture were studied during pressure or ionophoretic applications of ACh, using the 'whole-cell' and 'outside-out' configurations of the patch clamp technique. In standard salines, ACh evoked whole-cell currents of -38 pA to -1 nA at -60 mV, which had a reversal potential (EACh) of -741 + 0-6 mV. The ACh current-voltage relationship was characteristically linear at negative holding potentials and biphasic at positive holding potentials, displaying a region of almost zero slope conductance between 0 and + 40 mV followed by a region of positive slope conductance at more positive potentials.2. Relative permeation to cations was examined. Substitution of external Na+ by sucrose resulted in a -42 mV shift of EACh for a 10-fold reduction in [Na+]o. Using isotonic substitutions, the permeability ratios (relative to Na+) for monovalent cations were determined to be 132+0-02 for Cs' (n = 11), 103+0-02 for Li+ (n = 8) and 018 + 002 for Tris' (n = 7). Elevated external Ca2+ salines were found to shift EACh to more positive potentials, especially in the presence of low external Na+.3. The nicotinic agonists nicotine, tetramethylammonium and lobeline evoked inward currents in bovine chromaffin cells. In contrast, decamethonium and the muscarinic agonist, methacholine, had no effect.4. The nicotinic antagonists mecamylamine, trimetaphan, (+ )-tubocurarine and hexamethonium caused dose-dependent reductions in the amplitude of ACh-evoked inward currents. The estimated IC50's were 0-25, 0 33, 0-63 and 2'2 1am respectively, for cells voltage clamped at -60 mV. High concentrations (> 2 /tM) of the muscarinic antagonist, atropine, also produced a dose-dependent reduction in the amplitude of ACh-induced currents.5. Inhibition by trimetaphan was voltage independent. With the other drugs the antagonism was voltage sensitive, increasing with membrane hyperpolarization. The voltage sensitivity was most marked for hexamethonium. Neither hexamethonium nor mecamylamine were found to depress ACh-evoked outward currents at concentrations which severely depressed inward currents. In addition to its

The naturally occurring progesterone metabolites 5β-pregnan-3α-ol-20- one and 5β-pregnane-3, 20-dione reversibly enhance membrane currents elicited by locally applied GABA in bovine adrenomedullary chromaffin cells. Such potentiation was not influenced by the benzodiazepine antagonist Ro 15-1788. At concentrations in excess of those necessary to evoke potentiation of GABA currents, 5β-pregnan-3α-ol-20-one and 5β-pregane-3, 20-dione directly activated a membrane conductance. The resulting currents were potentiated by phenobarbitone and diazepam, and abolished by the GABA A -receptor antagonist, bicuculline. On out­side-out membrane patches, 5β-pregnan-3a-ol-20-one and 5β-pregnane-3, 20-dione activated single channel currents of similar amplitude to those evoked by GABA. The results suggest that certain naturally occurring steroids potentiate the actions of GABA and, additionally, directly activate the GABA A receptor.

Scientists and regulators in Europe and the United States continue to seek methods and strategies to improve knowledge on rational use of medicines for pregnant and breastfeeding populations, an important subset of women's health. Regulatory agencies have made strides toward improvement, but much more is needed. Recognizing the importance of international collaboration, we have begun to consider how to address these important public health issues more globally. The health of the child begins with the health of the mother.

1 The desensitizing acetylcholine (ACh) response of bovine chromaffin cells maintained in culture was examined using rapid agonist applications (of 2 s duration) which imposed nominal drug concentrations within 50 ms. This study was aimed, firstly, at identifying which of the o3, a4 and a7 subunits known to be present in these cells is predominant in the ACh-evoked response and secondly, on the effects on these neuronal nicotinic ACh receptors (AChR) of cyclothiazide (CT), an agent acting as a modulator of a gating desensitization site on other ligand-gated channels.2 Locally applied 100 JAM ACh evoked peak currents ('ACh) of -1.5 ± 0.1 nA (n = 83) at a holding potential of -60 mV. The ACh dose-response curve yielded an estimated EC50 of 60 gAM. This current was not sustained but desensitized during the application period; it displayed strong inward rectification, but desensitized equally whether the evoked current was inward or outward going. The latter observation excludes a4 as a major contributor to the recorded current. Because the response was almost insensitive to a 1 JM x-bungarotoxin pretreatment (ACh = -1.2 ± 0.1 nA; n = 6), and because 1, 1-dimethyl-4-phenylpiperazinium (DMPP) works as a potent agonist (peak current =-1.9 nA, n = 2 for 100 JAM DMPP), the a7 subunit is also a minor contributor to the response. Taken together, these observations suggest a dominant a3 type of response. 3 Triple exponential fits were used to describe the characteristics of the ACh-evoked currents; one component to fit the rising phase, with 2 components to describe the decay phase. The decay times were 100 ms and 4 s for the fast and slow components respectively. The rate of the slow decay component increased systematically with recording time, approximately doubling from its initial value within 20-40 min. Furthermore there was a gradual rundown of the response, seen first as a loss of the late component of the current, measured at 2 s, with the peak current amplitude decreasing later in the recording. 4 CT, when coapplied with ACh, produced a dose-dependent inhibition of the ACh-evoked peak current. The effect showed little voltage-dependency with 100 JAM CT producing 46 ± 5% (s.d.; n = 3) and 47 ± 8% (s.d.; n = 7) inhibition at -100 and -60 mV respectively. At + 60 mV, inhibition was estimated to be 26 ± 7% (s.d.; n = 3). 5 After pre-exposure of the cells to CT by bath application, 10 and 30 AM CT produced poorly reversible 20 ± 9% (n = 7) and 42 + 5% (n = 4) inhibitions of the peak current respectively. There were no discernible effects on the fitted decay constants at any CT concentration tested, although an increased inhibitory effect of CT was observed at higher concentrations (100 JAM) on the amplitude of the late component measured at 2 s.6 Similar effects were observed in conditions chosen to isolate the a3 type of receptor: namely when using DMPP as an agonist, or after a-bungarotoxin pretreatment. 7 The 2,3-benzodiazepine, GYKI 53655, is known to antagonize the action of CT on AMPA receptors. Coapplication of...