PubMed Health⌕ Search

Biomedical subjects

S J Quinn

Publications and source records attributed to S J Quinn.

16 recordsLinked to original sources
PubMed1992

Regulation of intracellular pH in single rat zona glomerulosa cells.

The cytosolic pH (pHi) regulation of rat adrenal zona glomerulosa (ZG) cells was studied using single-cell spectrofluorimetry. Basal pHi was similar for cells incubated in the absence or presence of the HCO3(-)-CO2 buffering system. In the absence of HCO3-, inhibition of the Na(+)-H+ exchanger by dimethylamiloride (DMA) or removal of extracellular Na+ produced substantial acidification of basal pHi. In the presence of HCO3-, neither maneuver affected basal pHi. However, removing extracellular Cl- produced a prompt alkalinization not observed in the absence of HCO3-. Alkalinizing mechanisms were examined by monitoring pHi recovery from an acid load imposed by the NH4Cl pulse technique. In the absence of HCO3-, Na+ removal or DMA addition blocked greater than 80% of pHi recovery. In the presence of HCO3-, 34% of the pHi recovery rate was inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), 34% by DMA, and 72% by Na+ removal plus DIDS. Therefore both Na(+)-H+ and anion exchangers are active in these cells, working independently to maintain basal pHi. In the absence of HCO3-, Na(+)-H+ exchange is principally responsible for pHi recovery from an acid load. In HCO(3-)-containing medium, such recovery is shared by Na(+)-H+ and Cl(-)-HCO3- exchange.

Acids↗
PubMed1992

Calcium channels and control of cytosolic calcium in rat and bovine zona glomerulosa cells.

Rat and bovine adrenal zona glomerulosa (ZG) cells possess a low-threshold, voltage-dependent Ca2+ current that was characterized using whole cell voltage clamp techniques. Activation of this current is observed at membrane potentials above -80 mV with maximal peak Ca2+ current elicited near -30 mV. Inactivation of the Ca2+ current was half-maximal between -74 and -58 mV, depending on the external Ca2+ concentration and was nearly complete at -40 mV. The voltage dependency of the current indicates that a calcium current could be sustained at membrane potentials between -80 and -40 mV and thereby elevates cytosolic calcium (Cai) levels. Under basal conditions, Cai is stable in single rat ZG cells, whereas more than half of the bovine ZG cells produce repeated Cai transients. These Cai transients, which are blocked by removal of external Ca2+ or addition of Ni2+, are likely due to repetitive electrical activity in bovine ZG cells. Cai responses can be elicited by small increases in external K+ concentration (5-10 mM) in both rat and bovine ZG cells, indicating the opening of low-threshold Ca2+ channels. However, these Cai changes remain robust at high external K+ concentrations (20-40 mM). In experiments combining Cai measurements and whole cell voltage clamp, a steep dependence of Cai on membrane potential was revealed beginning at depolarizing voltages near a holding membrane potential of -80 mV. A maximal increase in Cai occurred near -30 mV (equivalent to an external K+ concentration of 40 mM), a membrane voltage at which sustained current through low-threshold Ca2+ channels should be negligible. These data raise the possibility of additional voltage-dependent pathways for Ca2+ influx.

4-Aminopyridine↗
PubMed1992

K+ channels in adrenal zona glomerulosa cells. I. Characterization of distinct channel types.

Four distinct types of K+ channels were identified in rat and bovine adrenal zona glomerulosa (ZG) cells and characterized using single-channel recording techniques. Inward rectifier channels were the most frequently observed K+ channel types in the membrane patches of both rat and bovine ZG cells. The slope conductance of the inward current was 42 pS with an extracellular K+ concentration of 150 mM. The probability of the open state of these channels increased with depolarization. With the use of inside-out membrane patches with symmetric 150 mM K+ solutions, the rectifying behavior was found to require Mg2+ on the intracellular side of the membrane. Delayed rectifier K+ channels with conductances of 27 and 48 pS were found with rat ZG cells. These channels persisted with prolonged positive voltage steps and showed long mean open times with increasing depolarization. Transient outward currents with a conductance of 28 pS were observed only in bovine ZG cells. These channels showed substantial inactivation during positive voltage steps of 250 ms duration. Ca(2+)-activated K+ channels with a large conductance (228 pS) were identified in rat and bovine ZG cells. These different classes of K+ channels may be important for the control of resting membrane potential and the generation of action potentials, thus participating in the regulation of Ca2+ influx and aldosterone secretion in ZG cells.

Animals↗
PubMed1992

Single K+ channels in adrenal zona glomerulosa cells. II. Inhibition by angiotensin II.

The effects of angiotensin II (ANG II) on single K+ channels were studied in rat and bovine adrenal zona glomerulosa (ZG) cells, using the patch-clamp technique. ANG II (0.1-10 nM) induced substantial inhibition of inward rectifier and delayed rectifier K+ channel activities in rat and bovine ZG cells. Analysis of single-channel activities showed that the ANG II-induced channel-blocking effect involved reductions in the probability of the open state (Po) and the mean open time. The changes in these channel parameters occurred at all test voltages, indicating that the effect of ANG II was voltage independent. ANG II could not interact directly with the extracellular sides of the membranes in these experiments using cell-attached patches. Therefore, the effect of ANG II on K+ channels must occur through an indirect cytosolic transduction pathway. The ANG II-induced block of K+ channels will result in membrane depolarization, which may activate voltage-dependent Ca2+ channels, thereby increasing cytosolic free Ca2+ and stimulating aldosterone secretion. These channel-modulating actions of ANG II may be an important step in the initial sequence of events underlying its transduction mechanism.

Angiotensin II↗
PubMed1991

ANG II blocks potassium currents in zona glomerulosa cells from rat, bovine, and human adrenals.

Angiotensin II (ANG II) is a principal secretagogue of adrenal zona glomerulosa (ZG) cells. The transduction process includes a depolarization of the plasma membrane and the activation of calcium influx. The ANG II-induced depolarization is associated with an increase in total membrane resistance. To directly address the mechanism underlying these observations, we examined the effect of ANG II on K+ currents of rat, bovine, and human ZG cells, using whole cell patch clamp. Although some differences were seen in the characteristics of K+ currents between species, ANG II consistently blocked outward currents in ZG cells [rat: 47.1 +/- 4.5% (SE), n = 17; bovine: 38.6 +/- 3.3%, n = 21; and human: 13-63%, n = 3]. With the use of the cell-attached mode, single-channel recordings in bovine ZG cells demonstrated K+ channels that were reversibly blocked when ANG II was added to the bath solution. This indicates that the block of K+ channels by ANG II involves a diffusible intracellular messenger rather than a direct receptor-channel interaction. The decreased conductance of K+ can account for the ANG II-induced membrane depolarization.

Angiotensin II↗
PubMed1991

Cytosolic calcium responses of single rMTC 44-2 cells to stimulation with external calcium and potassium.

Few endocrine tissues can detect changes in the extracellular Ca2+ concentration within the physiological range and modify their hormone secretion accordingly. A rat cell line of C-cell origin (rMTC 44-2) secretes calcitonin and neurotensin in response to small increases in external Ca2+. To better understand the mechanism of extracellular Ca2+ sensing in this cell type, we studied single fura-2-loaded rMTC 44-2 cells perfused with increasing concentrations of Ca2+ and K+. In the basal state (Ca2+ = 0.5 mM), cytosolic Ca2+ levels were 53 nM, with 27% of the cells having spikes or oscillations. With elevation of the external Ca2+ to between 0.5 and 4 mM, 84% of the cells showed a rapid (less than 5 s) rise in cytosolic Ca2+ to values 2- to 10-fold higher than basal levels. Most of the responding cells exhibited complex patterns of cytosolic Ca2+ fluctuations, including oscillations with frequencies varying from less than 1/min to as many as 6/min. When averaged over time, the cytosolic Ca2+ of individual cells showed a dose-dependent response with changes in external Ca2+, resembling the relationship between extracellular Ca2+ and calcitonin secretion. With continued or repeated stimulation, the spike amplitude often declined. These cytosolic Ca2+ responses were attenuated in the presence of the Ca(2+)-channel blockers cadmium and nifedipine. Cytosolic Ca2+ responses to perfusion with elevated K+ (20 mM) were similar in waveform to those seen with Ca2+ stimulation. Most cells displayed cytosolic Ca2+ changes in response to both ionic secretagogues when stimulated with external Ca2+ or K+.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Kinetics of cytosolic calcium and aldosterone responses in rat adrenal glomerulosa cells.

To evaluate the relationship between cytosolic calcium (Cai) and aldosterone production, rat adrenal zona glomerulosa (ZG) cells were studied during long-term stimulation by different secretagogues. Cai was measured in single ZG cells using microspectrofluorimetry, and aldosterone was determined in cell populations using a superfusion system. For external potassium (K+), Cai increases are sustained, with only a slight decrement over time, a feature shared by aldosterone production. The relationship between aldosterone output and Cai is nonlinear, with a Cai value for half-maximal stimulation of approximately 500 nM. Furthermore, the sustained changes in Cai with external K+ indicate that ZG cells can use an amplitude-based Cai signal to stimulate aldosterone production. Cai changes stimulated by angiotensin-II (Ang-II) show a complex dose-response pattern, with high concentrations (greater than or equal to 1 nM) of Ang-II eliciting a peak-plateau signal and lower doses (0.1 nM to 10 pM) producing repeated Cai oscillations. The peak amplitude of the Cai response in individual cells is not dose dependent, with the ZG cell experiencing peak levels repeatedly at the lowest Ang-II concentrations. However, the Cai transients are more frequent with increasing Ang-II concentrations between 0.1 nM and 10 pM. When integrated over time, the mean Cai signal also shows only modest dose-dependency during the sustained phase of Ang-II stimulation. Unlike the integrated Cai signal, aldosterone production increases steeply between 10 pM and 0.1 nM Ang-II, indicating that the Cai signal is likely to be frequency-based. Conversely, the steroid response to high Ang-II closely mirrors the kinetics of the more sustained Cai signals, including the diminished Cai and aldosterone levels during sustained stimulation with the highest Ang-II doses. Arginine vasopressin stimulated Cai and aldosterone responses, which closely resemble those elicited by 0.1 nM Ang-II, except that both Cai and aldosterone return to basal values within 20 min of continuous presentation of arginine vasopressin. Each ZG secretagogue produces a distinct pattern of Cai and aldosterone response. In addition, Cai response patterns can be divided into two general classes: a sustained Cai response, which appears to modulate cell activation by the amplitude of the Cai signal, and an oscillating Cai response, which uses the frequency of the Cai transients to control the magnitude of stimulation.

Aldosterone↗
PubMed1990

Cytosolic calcium and aldosterone response patterns of rat adrenal glomerulosa cells stimulated by vasopressin: comparison with angiotensin II.

Cytosolic calcium (Cai) responses to arginine vasopressin (AVP) and angiotensin-II (Ang II) were examined in single rat adrenal zona glomerulosa (ZG) cells by monitoring fura-2 fluorescence with microspectrofluorimetry. ZG cells displayed dose-dependent Cai responses to a wide range of AVP and Ang II concentrations, starting from a threshold of 1 nM for AVP and less than 5 pM for Ang II. A dose-dependent delay of the onset of the Cai response was observed with both hormones. The response delay for Ang II was consistently briefer than that for the same concentration of AVP, showing a 2-3 log unit separation in the dose-response relations. After the delay, cells typically responded with an abrupt increase in Cai, which peaked within 15 sec. The amplitude of the peak Cai rise showed little dependency on AVP or Ang II concentration. At most AVP concentrations, the response consisted of Cai oscillations, with apparent fusion of these Cai oscillations at the highest AVP concentrations (1-0.1 microM). Similar oscillatory behavior was found with stimulations by much lower Ang II concentrations (0.5 nM to 5 pM). There appeared to be a 2-3 log unit shift in the sensitivity toward AVP and Ang II when Cai responses were compared. Sixty percent of ZG cells were responsive to AVP, while more than 90% displayed an elevation of Cai with Ang II. The Cai and steroid responses to 100 nM AVP and 100 pM Ang II were compared, since these two doses are reported to stimulate the phosphoinositide system to a similar extent. Individual ZG cells tested with both hormones responded with equivalent peak Cai changes, but a slightly longer response delay for AVP. The mean Cai response and aldosterone production for each secretagogue displayed parallel kinetics during 30-min stimulations. After initial oscillations, the Cai response returned to control values within 15 min of 100 nM AVP application. Likewise, the steroid output was transient. In contrast, 100 pM Ang II produced maintained Cai oscillations as well as a sustained and substantially greater aldosterone production for the same period of application. In conclusion, the disparate steroidogenic effects of AVP and Ang II appear to result from distinctly different Cai responses elicited during maintained secretagogue stimulation.

Aldosterone↗
PubMed1988

Calcium oscillations in single adrenal glomerulosa cells stimulated by angiotensin II.

The cytosolic calcium (Ca2+i) response to angiotensin II (Ang II) was examined in single rat zona glomerulosa cells by monitoring fura-2 fluorescence with microspectrofluorimetry. Ang II concentrations ranged from 5 X 10(-12) to 5 X 10(-8) M. The mean peak Ca2+i increase was similar at all Ang II concentrations (205 +/- 11 nM), with a significant difference (P less than 0.05) found only between 5 X 10(-12) M (151 +/- 16 nM) and 5 X 10(-9) M (236 +/- 24 nM). Striking differences over the range of Ang II concentrations were found in the Ca2+i response kinetics. A dose-dependent delay of the onset of the Ca2+i response was observed ranging from 2.6 +/- 0.3 sec at 5 X 10(-8) M to 181 +/- 27 sec at 5 X 10(-12) M Ang II. After the delay, cells typically responded with an abrupt increase in Ca2+i, complete within 15 sec. At low Ang II concentrations (5 X 10(-11) and 5 X 10(-12) M), a complex response was often observed consisting of Ca2+i oscillations. Higher Ang II concentrations gave some evidence of Ca2+i oscillation, especially at 5 X 10(-10) M where oscillations appeared fused. Above 5 X 10(-10) M Ang II, the initial Ca2+i increase decayed to an apparent steady-state value 38-40% of the peak response within 5 min; 5 X 10(-10) M Ang II produced a smaller decline to 63% of the initial Ca2+i increase. In contrast to cell population studies, assessment of individual glomerulosa cells demonstrates (i) a dose-dependent delay prior to a rapid increase in Ca2+i; (ii) a similar peak increase at most Ang II concentrations; (iii) greater sensitivity of the Ca2+i response; and (iv) a complex oscillating Ca2+i response in the physiological range of Ang II.

Adrenal Cortex↗
PubMed1988

Stressors and psychological symptoms of family practice residents and spouses.

Fifty-nine family practice residents and their spouses from one university-based and three community-based residency programs were studied to assess the frequency of stressful events in their lives and to quantify adverse psychosocial effects associated with that stress. A modified version of a questionnaire produced and tested by the University of Minnesota and the widely used, standardized Symptom Checklist-90 (SCL-90) were used to assess stress and psychological symptoms. There was a high correlation between high numbers of stressful events in the residents' and spouses' lives and high ratings of psychological symptoms. This finding was particularly true for the female residents. Overall, the residents' responses were near the mean for a nonpatient group used as a normative comparison on each of the nine subscales of the SCL-90 and on the overall mean for the entire scale. This finding indicated that the residents, although their lives were quite stressful, were handling the stress without major problems. The residents and their spouses also answered questions about 10 therapeutic interventions concerning stress and indicated which interventions they preferred.

Family Practice↗
PubMed1988

Regulation of aldosterone secretion.

Regulation of aldosterone secretion is complex both in terms of the number of secretagogues that can influence its biosynthesis and the number of second messengers utilized by these secretagogues (Table 1, Figure 1). ACTH primarily acts via the adenylate cyclase system through a stimulatory G protein; however, there is evidence that at low concentration it may also activate calcium influx and phospholipase C in some species. The primary effect of AII is activation of phospholipase C, which increases both calcium release from intracellular stores and calcium flux across the cell membrane and activates protein kinase C. Potassium depolarizes the membrane, thereby activating calcium flow through voltage-dependent calcium channels. It also directly or indirectly causes release of calcium from intracellular binding sites. A small change in cAMP levels may also be involved in the sustained secretory response to potassium. Species variation in the regulation of aldosterone secretion probably exists; the control mechanisms in the human appear to be closer to those in the rat than to those in cow and sheep. How changes in dietary sodium and potassium modify aldosterone secretion and the adrenal's responsiveness to secretagogues remains unclear. Yet these effects may be of considerable importance, both in terms of understanding the overall regulation of aldosterone secretion and in resolving the discrepancies in the results obtained under different experimental conditions.

Aldosterone↗
PubMed1988

Calcium response of single adrenal glomerulosa cells to external potassium.

The cytosolic calcium (Cai2+) response to external potassium (K+) was examined in single rat zona glomerulosa (ZG) cells by monitoring fura-2-fluorescence with microspectrofluorometry and digital imaging microscopy. The majority (68%) of morphologically identified ZG cells demonstrated an increase in Cai2+ during K+ stimulation. Cai2+ rose monotonically from a mean basal level of 232 +/- 15 to 285 +/- 37 nM at 5 mM and 680 +/- 60 nM at 10 mM K+ for responsive ZG cells. The Cai2+ response was largely (greater than 90%) inhibited by nominal zero calcium or 1 mM cadmium and substantially modified in the presence of 10(-5) M nifedipine. The response kinetics were characterized by a rising phase that depended on the size of the Cai2+ change, with larger increases associated with a faster onset. Cai2+ approached a plateau level that was sustained for the duration of K+ stimulation from 1 to 5 min. Cai2+ appeared to be more uniformly distributed across the cell under resting conditions than during stimulation. Assessment of the Cai2+ response in single ZG cells documents 1) a majority, but not all, of ZG cells respond to K+, 2) simple kinetics consisting of a rapid onset and sustained plateau Cai2+ level, 3) a dose-dependent Cai2+ increase in the physiological range of K+, and 4) inhibition by calcium channel blockers and sensitivity to small increases in K+ consistent with activation of low-threshold calcium channels.

Animals↗
PubMed1987

Electrical properties of isolated rat adrenal glomerulosa and fasciculata cells.

Passive and active electrical properties of isolated rat adrenal glomerulosa and fasciculata cells were studied by intracellular voltage-recording and constant current stimulation. The average resting membrane potential was -78.9 +/- 4.2 mV for glomerulosa cells and -77.8 +/- 5.0 mV for fasciculata cells. The response of the membrane potential to changes in external K+ concentration was stable and reversible for changes up to 28 mM and was independent of external Cl-. The relationship between membrane potential and the log of external K+ concentration was linear between 4 and 28 mM, and the membrane potential could be predicted by a simplified form of the constant field equation with a [K]i of 138.5 mM and a PNa/PK of 0.015 for glomerulosa cells and a [K]i of 112.4 mM and a PNa/PK of 0.011 for fasciculata cells. Under current clamp conditions, both cells demonstrated a nonlinear relationship between membrane voltage and applied current for depolarizing current steps. Depolarizing current pulses elicited a regenerative response and were followed by a rectifying steady state potential. The maximum rate of rise and the peak amplitude of the regenerative response were increased by prior hyperpolarization below the resting membrane potential and decreased by depolarization. The regenerative response was unaffected by the removal of Na+. Elevated Ca2+ concentrations increased the rate of rise, peak amplitude, and rate of fall, but decreased the duration of the regenerative response. The regenerative response was maintained upon replacement of Ca2+ with Sr2+ or Ba2+, but was inhibited by Mn2+ or Co2+. Regenerative responses elicited in both glomerulosa and fasciculata cells exhibited similar characteristics. The results suggest the ionic mechanism underlying the regenerative response to be a voltage-dependent Ca2+ conductance. Both adrenal glomerulosa and fasciculata cells demonstrate electrical properties in common with other excitable cells. They are good K+ sensors with regard to their membrane potential, approaching the maximum sensitivity expected for a membrane exclusively permeable to K+. In addition, the Ca2+ regenerative response, which has been identified in both adrenal glomerulosa and fasciculata cells, may be involved in secretagogue stimulation of steroidogenesis.

Adrenal Cortex↗
PubMed1987

Electrophysiological responses to angiotensin II of isolated rat adrenal glomerulosa cells.

The membrane response of isolated rat glomerulosa cells to the application of angiotensin II (A II) has been studied using intracellular voltage measurements. The membrane response is biphasic. The first, brief phase involves an increase in membrane conductance and a hyperpolarization from the resting membrane potential. The second, long-lasting phase is characterized by a large decrease in membrane conductance and a depolarization from the resting membrane potential. The reversal potential for the second phase is -94 +/- 1.2 mV, and a linear relationship between reversal potential and external K+ indicates that the A II-mediated response is predominantly inhibition of K+ permeability. The A II response can be elicited when external Ca2+ is replaced by Sr2+ or Ba2+, but the response is inhibited when Mn2+ is added to the bath or when stimulated in a Ca2+-free solution. A II appears to inhibit at least two conductances, when the cell is stimulated by long current steps. External application of A II inhibited the Ca2+ regenerative response found in glomerulosa cells in a dose-dependent manner. The rate of rise of the regenerative response was greatly attenuated by A II; half-maximal inhibition was produced by about 10(-9) M A II. In addition, rectification, evident at voltages more positive than -60 mV during current stimulation, was also inhibited. In conclusion, A II causes rat glomerulosa cells to depolarize due to the inhibition of resting K+ permeability. Action potential activity is not observed during A II-mediated membrane depolarization; rather, both Ca2+ and K+ conductances appear to be inhibited during A II application.

Action Potentials↗