No abstract

The adrenal medulla chromaffin cells (AMCs) secrete catecholamines in response to various types of stress. We examined the hypoxia-sensitivity of catecholamine secretion by rat foetal chromaffin cells in which the innervation by the splanchnic nerve is not established. The experiments were performed in primary cultured cells from two different ages of foetuses (F15 and F19). Membrane potential of AMCs was monitored with the patch clamp technique, and the catecholamine secretion was detected by amperometry. We found that: (1) AMCs from F19 foetuses showed hypoxia-induced catecholamine release. (2) This hypoxia-induced secretion is produced by membrane depolarization generated by an inhibition of Ca(2+)-activated K(+) current [I (K(Ca))] current. (3) Chromaffin precursor cells from F15 foetuses secrete catecholamine. The quantal release is calcium-dependent, but the size of the quantum is reduced. (4) In the precursor cells, a hypoxia-induced membrane hyperpolarization is originated by an ATP-sensitive K(+) current [I (K(ATP))] activation. (5) During the prenatal period, at F15, the percentage of the total outward current for I (K(ATP)) and I (K(Ca)) was 50 and 29.5%, respectively, whereas at F19, I (K(ATP)) is reduced to 14%, and I (K(Ca)) became 64% of the total current. We conclude that before birth, the age-dependent hypoxia response of chromaffin cells is modulated by the functional activity of K(ATP) and K(Ca) channels.

The rhizome of Curcuma longa (turmeric) is often used in Asia as a spice and as a medicine. Its most well-studied component, curcumin, has been shown to exhibit poor bioavailability in animal studies and clinical trials. We hypothesized that the presence of lipophilic components (e.g., turmerones) in turmeric extract would affect the absorption of curcumin. The effects of turmerones on curcumin transport were evaluated in human intestinal epithelial Caco-2 cells. The roles of turmerones on P-glycoprotein (P-gp) activities and mRNA expression were also evaluated. Results showed that in the presence of α- and aromatic turmerones, the amount of curcumin transported into the Caco-2 cells in 2 hours was significantly increased. α-Turmerone and verapamil (a P-gp inhibitor) significantly inhibited the efflux of rhodamine-123 and digoxin (i.e., inhibited the activity of P-gp). It is interesting that aromatic turmerone significantly increased the rhodamine-123 efflux and P-gp (MDR1 gene) mRNA expression levels. The effects of α- and aromatic turmerones on curcumin transport as well as P-gp activities were shown here for the first time. The presence of turmerones did affect the absorption of curcumin in vitro. These findings suggest the potential use of turmeric extract (including curcumin and turmerones), rather than curcumin alone, for treating diseases.

The gating kinetics and functions of low threshold T‐type current in cultured chromaffin cells from rats of 19–20 days gestation (E19‐E20) were studied using the patch clamp technique. Exocytosis induced by calcium currents was monitored by the measurement of membrane capacitance and amperometry with a carbon fibre sensor. In cells cultured for 1–4 days, the embryonic chromaffin cells were immunohistochemically identified by using polyclonal antibodies against dopamine β‐hydroxylase (DBH) and syntaxin. The immuno‐positive cells could be separated into three types, based on the recorded calcium current properties. Type I cells showed exclusively large low threshold T‐type current, Type II cells showed only high voltage activated (HVA) calcium channel current and Type III cells showed both T‐type and HVA currents. These cells represented 44 %, 46 % and 10 % of the total, respectively. T‐type current recorded in Type I cells became detectable at −50 mV, reached its maximum amplitude of 6.8 ± 1.2 pA pF−1 (n= 5) at −10 mV and reversed around +50 mV. The current was characterized by criss‐crossing kinetics within the −50 to −30 mV voltage range and a slow deactivation (deactivation time constant, τd= 2 ms at −80 mV). The channel closing and inactivation process included both voltage‐dependent and voltage‐independent steps. The antihypertensive drug mibefradil (200 nm) reduced the current amplitude to about 65 % of control values. Ni2+ also blocked the current in a dose‐dependent manner with an IC50 of 25 μm. T‐type current in Type I cells did not induce exocytosis, while catecholamine secretion by exocytosis could be induced by HVA calcium current in both Type II and Type III cells. The failure to induce exocytosis by T‐type current in Type I cells was not due to insufficient Ca2+ influx through the T‐type calcium channel. We suggest that T‐type current is expressed in developing immature chromaffin cells. The T‐type current is replaced progressively by HVA calcium current during pre‐ and post‐natal development accompanying the functional maturation of the exocytosis mechanism.