What ions does the NKA transport, and in which directions?
NKA transports 3 Na+ out of the cell and 2 K+ into the cell
Why does the NKA require ATP?
- it is moving these ions against their concentration gradient, so it takes energy to accomplish
- is going against entropy, so much invest ATP
What is secondary active transport?
- uses the Na+ gradient to move other molecules in or out of the cell
- there are transporters that move other molecules into the cell at the same time as Na+ or that move other molecules out of the cell while moving Na+ into the cell
- by transporting Na+ out of the cell and maintaining that gradient, it ensures that these transporters will always also be transporting these other molecules via this secondary active transport
What molecules does the NKA help transport by secondary active transport?
H+, amino acids, glucose
-also drives waste excretion, pH regulation, nutrient uptake, cell volume regulation, action potentials, neurotransmitter reuptake, regulating salts and water
What are the apical and the basolateral membrane within a cell?
- apical is the side in contact with the external medium
- basolateral is the side in contact with the blood
Which environments and situations are associated with hypoxia in aquatic environments?
- nighttime in tide pools, mangroves, coral reefs, kelp forests
- low tide
- permanent hypoxia in OMZs
- seasonal hypoxia caused by upwelling
What are the three general mechanisms to cope with hypoxia?
- enhance O2 uptake rate
- save energy
- obtain energy using anaerobic metabolic pathways
What happens to ATP supply and demand in hypoxia-tolerant organisms? And in hypoxia-intolerant organisms?
- in hypoxia-tolerant organisms, they decrease their ATP demand such that their supply is still sufficient to satisfy it. This allows them to survive with minimal ATP for a longer period of time
- in hypoxia-intolerant organisms, they are not able to decrease their ATP demand and the supply cannot keep up with it, leads to cell damage and cell death quickly
What is metabolic suppression? What are the main processes that get suppressed?
- downregulating ATP consumption in a regulated manner by suppressing processes that require ATP but are not essential for survival
- protein synthesis, protein breakdown, gluconeogenesis, and urea synthesis are all suppressed largely
- NKA suppressed the least due to high importance
Explain mechanisms in respiratory surfaces and respiratory pigments that help maximize oxygen uptake and delivery during hypoxia. Give examples of organisms that use those strategies.
- low P50 means the organism has high oxygen affinity and can better take advantage of the oxygen that is present
- large gill SA increases the amount of oxygen that can be taken up (EX: vampire squid has much higher SA than other cephalopods)
- reduced activity means lowered demand, so the ATP can be saved for necessary functions
- tambaqui has a highly vascularized lower lip that allows it to skim oxygen from the surface
- uses hemocyanin, as it does better in oxygen-poor areas because it has higher oxygen affinity (EX: vampire squid)
Compare and contrast the strategies used by crucian carp, Amazonic fishes, and vampire squid during hypoxia/anoxia.
All:
- very low P50
- High gill surface area
- Reduced locomotion and general activity levels
Crucian Carp:
-produces ethanol to replenish NAD+ and continue fermentation, ethanol diffuses out of lungs
Amazonian Fishes:
- High levels of hemoglobin and red blood cells
- High ability to produce ATP using fermentative pathways (end product lactate)
- High ability to counteract or withstand acidification
- Other respiratory surfaces (tambaqui has lower lip)
Vampire Squid:
- Neutrally buoyant, low metabolic rates
- uses hemocyanin while other two have hemoglobin
- Fermentative pathways not known (but probably robust)
Crucian carp: where is lactate produced during anoxia? Where is it converted to ethanol? What are the advantages?
- lactate produced throughout the body as a side product of fermentation
- converted to ethanol in muscle cells
- this requires ATP but consumes H+ and replenishes NAD+ to allow more fermentation to occur
- the ethanol can then diffuse out from the gills, so the waste product has been excreted
- allows anoxic survival without acidification and a buildup of lactate.
Mention mechanisms that allow animals survive in hypoxia, but are not useful in anoxia, and explain why.
- the tambaqui skimming the surface for more oxygen would not be beneficial if it was fully anoxic
- more hemoglobin/RBCs would not help in anoxia as there would be nothing to bind to
- high gill SA is also no more helpful when there is no oxygen to diffuse across the membrane
From a metabolic perspective, what are the challenges experienced by the vampire squid?
- feeds only on detritus, which expends little energy but also provides little nutrients
- must live in permanent hypoxia, difficult to repay any oxygen debt incurred
How does the vampire squid match ATP supply and demand?
- takes many steps to lower ATP demand in order to be able to meet it
- low metabolic rates => lowest mass-specific MR of all deep-sea cephalopods
- weak musculature, change from jet propulsion to fin swimming (less active, but it requires less energy)
- neutrally buoyant => saves energy (thanks to ammonium accumulation in tissues, will study this in future lectures)
- gill => increased surface area
- hemocyanin with low P50 (high affinity for O2) => efficiently extracts O2 from the water
