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Oda GM, Leite CAC, Abe AS, Klein W. Effects of different levels of hypoxia and hypercarbia on ventilation and gas exchange in Boa constrictor amaralis and Crotalus durissus (Squamata: Serpentes). Respir Physiol Neurobiol 2021; 294:103747. [PMID: 34302991 DOI: 10.1016/j.resp.2021.103747] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Revised: 07/05/2021] [Accepted: 07/18/2021] [Indexed: 10/20/2022]
Abstract
Ventilation and gas exchange have been studied in relatively few species of snakes, especially regarding their response to environmental hypoxia or hypercarbia. We exposed Crotalus durissus (N = 6) and Boa constrictor (N = 6) to decreasing levels of oxygen (12, 9, 6, 3 % O2) and increasing levels of carbon dioxide (1.5, 3.0, 4.5, 6.0 % CO2) and analyzed the effect of the different gas mixtures on ventilation and gas exchange using open-flow respirometry. Neither hypoxia nor hypercarbia significantly altered the duration of expiration or inspiration, nor their proportions. Both hypoxia and hypercarbia increased minute ventilation, but the decrease in oxygen had a less pronounced effect on ventilation. Gas exchange under normoxic conditions was low and was not significantly affected by hypoxia, but hypercarbia decreased gas exchange significantly in both species. While B. constrictor maintained its respiratory exchange ratio (RER) under hypercarbia between 0.5 and 1.0, C. durissus showed a RER above 1.0 during hypercarbia, due to a significantly greater CO2 excretion. The overall responses of both species to hypercarbia and especially to hypoxia were very similar, which could be associated to similar lifestyles as ambush hunting sit-and-wait predators that are able to ingest large prey items. The observed differences in gas exchange could be related to respiratory systems with macroscopically different structures, possessing only a tracheal lung in C. durissus, but two functional lungs in B. constrictor.
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Affiliation(s)
- Gustavo Marega Oda
- Programa de Pós-Graduação em Biologia Comparada, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, 14040-901, Ribeirão Preto, São Paulo, Brazil; Departamento de Ciências Fisiológicas, Universidade Federal de São Carlos, 13565-905, São Carlos, São Paulo, Brazil
| | - Cléo Alacantara Costa Leite
- Departamento de Ciências Fisiológicas, Universidade Federal de São Carlos, 13565-905, São Carlos, São Paulo, Brazil
| | - Augusto Shinya Abe
- Departamento de Zoologia, Universidade Estadual Paulista, 13506-900, Rio Claro, São Paulo, Brazil
| | - Wilfried Klein
- Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, 14040-901, Ribeirão Preto, São Paulo, Brazil.
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Koudrina N, Perry SF, Gilmour KM. The role of TASK-2 channels in CO 2 sensing in zebrafish ( Danio rerio). Am J Physiol Regul Integr Comp Physiol 2020; 319:R329-R342. [PMID: 32697653 DOI: 10.1152/ajpregu.00132.2020] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Peripheral chemosensitivity in fishes is thought to be mediated by serotonin-enriched neuroepithelial cells (NECs) that are localized to the gills of adults and the integument of larvae. In adult zebrafish (Danio rerio), branchial NECs are presumed to mediate the cardiorespiratory reflexes associated with hypoxia or hypercapnia, whereas in larvae, there is indirect evidence linking cutaneous NECs to hypoxic hyperventilation and hypercapnic tachycardia. No study yet has examined the ventilatory response of larval zebrafish to hypercapnia, and regardless of developmental stage, the signaling pathways involved in CO2 sensing remain unclear. In the mouse, a background potassium channel (TASK-2) contributes to the sensitivity of chemoreceptor cells to CO2. Zebrafish possess two TASK-2 channel paralogs, TASK-2 and TASK-2b, encoded by kcnk5a and kcnk5b, respectively. The present study aimed to determine whether TASK-2 channels are expressed in NECs of larval zebrafish and whether they are involved in CO2 sensing. Using immunohistochemical approaches, TASK-2 protein was observed on the surface of NECs in larvae. Exposure of larvae to hypercapnia caused cardiac and breathing frequencies to increase, and these responses were blunted in fish experiencing TASK-2 and/or TASK-2b knockdown. The results of these experiments suggest that TASK-2 channels are involved in CO2 sensing by NECs and contribute to the initiation of reflex cardiorespiratory responses during exposure of larvae to hypercapnia.
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Affiliation(s)
- N Koudrina
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | - S F Perry
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | - K M Gilmour
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
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Gilmour KM, Euverman RM, Esbaugh AJ, Kenney L, Chew SF, Ip YK, Perry SF. Mechanisms of acid–base regulation in the African lungfishProtopterus annectens. J Exp Biol 2007; 210:1944-59. [PMID: 17515420 DOI: 10.1242/jeb.02776] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYAfrican lungfish Protopterus annectens utilized both respiratory and metabolic compensation to restore arterial pH to control levels following the imposition of a metabolic acidosis or alkalosis. Acid infusion (3 mmol kg–1 NH4Cl) to lower arterial pH by 0.24 units increased both pulmonary (by 1.8-fold) and branchial (by 1.7-fold) ventilation frequencies significantly, contributing to 4.8-fold and 1.9-fold increases in,respectively, aerial and aquatic CO2 excretion. This respiratory compensation appeared to be the main mechanism behind the restoration of arterial pH, because even though net acid excretion(JnetH+) increased following acid infusion in 7 of 11 fish, the mean increase in net acid excretion, 184.5±118.5μmol H+ kg–1 h–1 (mean± s.e.m., N=11), was not significantly different from zero. Base infusion (3 mmol kg–1 NaHCO3) to increase arterial pH by 0.29 units halved branchial ventilation frequency, although pulmonary ventilation frequency was unaffected. Correspondingly, aquatic CO2 excretion also fell significantly (by 3.7-fold) while aerial CO2 excretion was unaffected. Metabolic compensation consisting of negative net acid excretion (net base excretion) accompanied this respiratory compensation, with JnetH+ decreasing from 88.5±75.6 to –337.9±199.4 μmol H+kg–1 h–1 (N=8). Partitioning of net acid excretion into renal and extra-renal (assumed to be branchial and/or cutaneous) components revealed that under control conditions, net acid excretion occurred primarily by extra-renal routes. Finally, several genes that are involved in the exchange of acid–base equivalents between the animal and its environment (carbonic anhydrase, V-type H+-ATPase and Na+/HCO –3 cotransporter) were cloned, and their branchial and renal mRNA expressions were examined prior to and following acid or base infusion. In no case was mRNA expression significantly altered by metabolic acid–base disturbance. These findings suggest that lungfish, like tetrapods, alter ventilation to compensate for metabolic acid–base disturbances, a mechanism that is not employed by water-breathing fish. Like fish and amphibians, however, extra-renal routes play a key role in metabolic compensation.
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Affiliation(s)
- K M Gilmour
- Department of Biology and Centre for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, ON, Canada.
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Perry SF, Gilmour KM. Acid-base balance and CO2 excretion in fish: unanswered questions and emerging models. Respir Physiol Neurobiol 2006; 154:199-215. [PMID: 16777496 DOI: 10.1016/j.resp.2006.04.010] [Citation(s) in RCA: 181] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2005] [Revised: 04/14/2006] [Accepted: 04/15/2006] [Indexed: 11/22/2022]
Abstract
Carbon dioxide (CO(2)) excretion and acid-base regulation in fish are linked, as in other animals, though the reversible reactions of CO(2) and the acid-base equivalents H(+) and HCO(3)(-): CO(2)+H(2)O<-->H(+)+HCO(3)(-). These relationships offer two potential routes through which acid-base disturbances may be regulated. Respiratory compensation involves manipulation of ventilation so as to retain CO(2) or enhance CO(2) loss, with the concomitant readjustment of the CO(2) reaction equilibrium and the resultant changes in H(+) levels. In metabolic compensation, rates of direct H(+) and HCO(3)(-) exchange with the environment are manipulated to achieve the required regulation of pH; in this case, hydration of CO(2) yields the necessary H(+) and HCO(3)(-) for exchange. Because ventilation in fish is keyed primarily to the demands of extracting O(2) from a medium of low O(2) content, the capacity to utilize respiratory compensation of acid-base disturbances is limited and metabolic compensation across the gill is the primary mechanism for re-establishing pH balance. The contribution of branchial acid-base exchanges to pH compensation is widely recognized, but the molecular mechanisms underlying these exchanges remain unclear. The relatively recent application of molecular approaches to this question is generating data, sometimes conflicting, from which models of branchial acid-base exchange are gradually emerging. The critical importance of the gill in acid-base compensation in fish, however, has made it easy to overlook other potential contributors. Recently, attention has been focused on the role of the kidney and particularly the molecular mechanisms responsible for HCO(3)(-) reabsorption. It is becoming apparent that, at least in freshwater fish, the responses of the kidney are both flexible and essential to complement the role of the gill in metabolic compensation. Finally, while respiratory compensation in fish is usually discounted, the few studies that have thoroughly characterized ventilatory responses during acid-base disturbances in fish suggest that breathing may, in fact, be adjusted in response to pH imbalances. How this is accomplished and the role it plays in re-establishing acid-base balance are questions that remain to be answered.
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Affiliation(s)
- S F Perry
- Department of Biology and Centre for Advanced Research in Environmental Genomics, University of Ottawa, 30 Marie Curie, Ottawa, Ont., Canada.
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Tattersall GJ, de Andrade DV, Brito SP, Abe AS, Milsom WK. Regulation of ventilation in the caiman (Caiman latirostris): effects of inspired CO2 on pulmonary and upper airway chemoreceptors. J Comp Physiol B 2005; 176:125-38. [PMID: 16283333 DOI: 10.1007/s00360-005-0034-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2005] [Revised: 08/23/2005] [Accepted: 09/20/2005] [Indexed: 10/25/2022]
Abstract
In order to study the relative roles of receptors in the upper airways, lungs and systemic circulation in modulating the ventilatory response of caiman (Caiman latirostris) to inhaled CO2, gas mixtures of varying concentrations of CO2 were administered to animals breathing through an intact respiratory system, via a tracheal cannula by-passing the upper airways (before and after vagotomy), or via a cannula delivering gas to the upper airways alone. While increasing levels of hypercarbia led to a progressive increase in tidal volume in animals with intact respiratory systems (Series I), breathing frequency did not change until the CO2 level reached 7%, at which time it decreased. Despite this, at the higher levels of hypercarbia, the net effect was a large and progressive increase in total ventilation. There were no associated changes in heart rate or arterial blood pressure. On return to air, there was an immediate change in breathing pattern; breathing frequency increased above air-breathing values, roughly to the same maximum level regardless of the level of CO2 the animal had been previously breathing, and tidal volume returned rapidly toward resting (baseline) values. Total ventilation slowly returned to air breathing values. Administration of CO2 via different routes indicated that inhaled CO2 acted at both upper airway and pulmonary CO2-sensitive receptors to modify breathing pattern without inhibiting breathing overall. Our data suggest that in caiman, high levels of inspired CO2 promote slow, deep breathing. This will decrease dead-space ventilation and may reduce stratification in the saccular portions of the lung.
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Affiliation(s)
- Glenn J Tattersall
- Department of Biology, Brock University, St Catharines, L2S 3A1, Ontario, Canada.
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Skovgaard N, Wang T. Cost of ventilation and effect of digestive state on the ventilatory response of the tegu lizard. Respir Physiol Neurobiol 2004; 141:85-97. [PMID: 15234678 DOI: 10.1016/j.resp.2004.04.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/14/2004] [Indexed: 11/15/2022]
Abstract
We performed simultaneous measurements of ventilation, oxygen uptake and carbon dioxide production in the South American lizard, Tupinambis merianae, equipped with a mask and maintained at 25 degrees C. Ventilation of resting animals was stimulated by progressive exposure to hypercapnia (2, 4 and 6%) or hypoxia (15, 10, 8 and 6%) in inspired gas mixture. This was carried out in both fasting and digesting animals. The ventilatory response to hypercapnia and hypoxia were affected by digestive state, with a more vigorous ventilatory response in digesting animals compared to fasting animals. Hypoxia doubled total ventilation while hypercapnia led to a four-fold increase in total ventilation both accomplished through an increase in tidal volume. Oxygen uptake remained constant during all hypercapnic exposures while there was an increase during hypoxia. Cost of ventilation was estimated to be 17% during hypoxia but less than 1% during hypercapnia. Our data indicate that ventilation can be greatly elevated at a small energetic cost.
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Affiliation(s)
- Nini Skovgaard
- Department of Zoophysiology, Aarhus University, Building 131, 8000 Aarhus C, Denmark
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Perry SF, Reid SG. Cardiorespiratory adjustments during hypercarbia in rainbow troutOncorhynchus mykissare initiated by external CO2receptors on the first gill arch. J Exp Biol 2002; 205:3357-65. [PMID: 12324545 DOI: 10.1242/jeb.205.21.3357] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYExperiments were performed to test the hypothesis that the marked ventilatory and cardiovascular responses to hypercarbia in rainbow trout Oncorhynchus mykiss arise from specific stimulation of chemoreceptors localised to the first gill arch. This was accomplished by measuring cardiorespiratory variables during acute hypercarbia (20 min at PCO2=8 mmHg; 1 mmHg=0.133 kPa) in fish subjected to selective bilateral extirpation of the first gill arch. The cardiovascular responses to hypercarbia in the intact fish included a significant bradycardia (from 75.0±1.6 to 69.0±2.0 beats min-1; means ± S.E.M.; N=16), an increase in dorsal aortic blood pressure (from 30.8±1.5 to 41.9±2.5 mmHg; N=16) and a rise in systemic vascular resistance (from 1.1±0.1 to 1.4±0.1 mmHg ml-1 kg-1 min-1; N=16). Removal of the first gill arch or pre-treatment with the muscarinic receptor antagonist atropine prevented the hypercarbic bradycardia without affecting the pressure or resistance responses. Correlation analysis,however, revealed shallow but significant inverse relationships between water PCO2 and cardiac frequency in both atropinised(r2=0.75) and gill-extirpated(r2=0.90) fish, suggesting a direct mild effect of CO2 on cardiac function. The ventilatory response to hypercarbia in the intact fish consisted of an increase in ventilation amplitude (from 0.62±0.06 to 1.0±0.13 cm; N=16) with no change in breathing frequency. Removal of the first gill arch lowered resting breathing frequency and prevented the statistically significant elevation of breathing amplitude. Gill extirpation, however, did not totally abolish the positive correlation between water PCO2 and ventilation amplitude (r2=0.84), suggesting the presence of additional(although less important) chemoreceptive sites that are not confined to the first gill arch. Plasma catecholamine levels were elevated during hypercarbia,and this response was unaffected by prior gill extirpation.To assess whether the CO2 chemoreceptors of the first gill arch were sensing water and/or blood PCO2, bolus injections of CO2-enriched water or saline were made into the buccal cavity or caudal vein, respectively. Injections of CO2-enriched water to preferentially stimulate external receptors evoked catecholamine release and cardiorespiratory responses that closely resembled the responses to hypercarbia. As in hypercarbia, extirpation of the first gill arch prevented the bradycardia and the increase in ventilation amplitude associated with externally injected CO2-enriched water. Except for a slight decrease in cardiac frequency (from 73.0±2.8 to 70.3±3.5 beats min-1; N=11), injection of CO2-enriched saline to preferentially stimulate internal chemoreceptors did not affect any measured variable. Taken together, these data indicate that, in rainbow trout, the bradycardia and hyperventilation associated with hypercarbia are triggered largely by external CO2chemoreceptors confined to the first gill arch.
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Affiliation(s)
- Steve F Perry
- Department of Biology, University of Ottawa, 50 Marie Curie, Ontario, Canada, K1N 6N5.
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Perry SF, McKendry JE. The relative roles of external and internal CO2versusH+ in eliciting the cardiorespiratory responses ofSalmo salarandSqualus acanthiasto hypercarbia. J Exp Biol 2001; 204:3963-71. [PMID: 11807114 DOI: 10.1242/jeb.204.22.3963] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYFish breathing hypercarbic water encounter externally elevated PCO2 and proton levels ([H+]) and experience an associated internal respiratory acidosis, an elevation of blood PCO2 and [H+]. The objective of the present study was to assess the potential relative contributions of CO2versus H+ in promoting the cardiorespiratory responses of dogfish (Squalus acanthias) and Atlantic salmon (Salmo salar) to hypercarbia and to evaluate the relative contributions of externally versus internally oriented receptors in dogfish.In dogfish, the preferential stimulation of externally oriented branchial chemoreceptors using bolus injections (50 ml kg–1) of CO2-enriched (4 % CO2) sea water into the buccal cavity caused marked cardiorespiratory responses including bradycardia (–4.1±0.9 min–1), a reduction in cardiac output (–3.2±0.6 ml min–1 kg–1), an increase in systemic vascular resistance (+0.3±0.2 mmHg ml min–1 kg–1), arterial hypotension (–1.6±0.2 mmHg) and an increase in breathing amplitude (+0.3±0.09 mmHg) (means ± s.e.m., N=9–11). Similar injections of CO2-free sea water acidified to the corresponding pH of the hypercarbic water (pH 6.3) did not significantly affect any of the measured cardiorespiratory variables (when compared with control injections). To preferentially stimulate putative internal CO2/H+ chemoreceptors, hypercarbic saline (4 % CO2) was injected (2 ml kg–1) into the caudal vein. Apart from an increase in arterial blood pressure caused by volume loading, internally injected CO2 was without effect on any measured variable.In salmon, injection of hypercarbic water into the buccal cavity caused a bradycardia (–13.9±3.8 min–1), a decrease in cardiac output (–5.3±1.2 ml min–1 kg–1), an increase in systemic resistance (0.33±0.08 mmHg ml min–1 kg–1) and increases in breathing frequency (9.7±2.2 min–1) and amplitude (1.2±0.2 mmHg) (means ± s.e.m., N=8–12). Apart from a small increase in breathing amplitude (0.4±0.1 mmHg), these cardiorespiratory responses were not observed after injection of acidified water.These results demonstrate that, in dogfish and salmon, the external chemoreceptors linked to the initiation of cardiorespiratory responses during hypercarbia are predominantly stimulated by the increase in water PCO2 rather than by the accompanying decrease in water pH. Furthermore, in dogfish, the cardiorespiratory responses to hypercarbia are probably exclusively derived from the stimulation of external CO2 chemoreceptors, with no apparent contribution from internally oriented receptors.
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Affiliation(s)
- S F Perry
- Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, Ontario, Canada K1N 6N5.
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